Conan

- Feature: Largely improved management of **environment variables**, declaration in `package_info()`,
definition in profiles, in command line, per package, propagation to consumers.
- Feature: New build helpers `AutotoolsBuildEnvironment`, `VisualStudioBuildEnvironment`, which
deprecate `ConfigureEnvironment`, with much better usage of environment variables
- Feature: New `virtualbuildenv` generator that will generate a composable environment with build
information from installed dependencies.
- Feature: New `build_id()` recipe method that allows to define logic to build once, and package
multiple times without building. E.g.: build once both debug and release artifacts, then package
separately.
- Feature: **Multi-config packages**. Now packages can provide multi-configuration packages, like
both debug/release artifacts in the same package, with `self.cpp_info.debug.libs = [...]` syntax.
Not restricted to debug/release, can be used for other purposes.
- Feature: new `conan config` command to manage, edit, display `conan.conf` entries
- Feature: Improvements to `CMake` build helper, now it has `configure()` and `build()` methods
for common operations.
- Feature: Improvements to `SystemPackageTool` with detection of installed packages, improved
implementation, installation of multi-name packages.
- Feature: Unzip with `tools.unzip` maintaining permissions (Linux, OSX)
- Feature: `conan info` command now allows profiles too
- Feature: new tools `unix_path()`, `escape_windows_cmd()`, `run_in_windows_bash()`, useful
for autotools projects in Win/MinGW/Msys
- Feature: new context manager `tools.chdir`, to temporarily change directory.
- Feature: CMake using `CMAKE_SYSTEM_NAME` for cross-compiling.
- Feature: Artifactory build-info extraction from traces
- Feature: Attach custom headers to artifacts uploads with an `artifacts.properties` file.
- Feature: allow and copy symlinks while `conan export`
- Fix: removing quotes in some cmake variables that were generating incorrect builds
- Fix: providing better error messages for non existing binaries, with links to the docs
- Fix: improved error messages if `tools.patch` failed
- Fix: adding `resdirs` to `cpp_info` propagated information, and cmake variables, for directories
containing resources and other data.
- Fix: printing error messages if a `--build` policy doesn't match any package
- Fix: managing VS2017 by `tools`. Still the manual definition of `vs150comntools` required.
- Bug fix: crashes when not supported characters were dumped to terminal by logger
- Bug fix: wrong executable path in Visual Studio generator

**NOTE**: It is important that you upgrade at least to 0.19.3 version if you are using remotes with packages that might be created with 0.20.0 version.

- Fix: backward compatibility for new environment variables. New features to be introduced in 0.20
will produce that `conaninfo.txt` will not be correctly parsed, and then the package would be "missing".
This will happen for packages created with 0.20 and consumed with older than 0.19.3

**NOTE**: It is important that you upgrade at least to this version if you are using remotes with packages
that might be created with latest conan releases (like conan.io).

- Bug fix: Fixed issue with remotes behind forwarding proxy
- Bug fix: Fixed `exports_sources` with nested folders bug

- Bug fix: Fixed issue with `conan copy` followed by `conan upload` due to the new `exports_sources`
feature.

- Feature: `exports_sources` allows to snapshot sources (like `exports`) but retrieve them strictly
when necessary, to build from sources. This can largely improve install times for package recipes
containing sources
- Feature: new configurable **tracer** able to create structured logs of conan actions: commands, API calls, etc
- Feature: new logger for `self.run` actions, able to log information from builds and other commands
to files, that can afterwards be packaged together with the binaries.
- Feature: support for **Solaris SunOS**
- Feature: `Version` helper improved with `patch, pre, build` capabilities to handle `1.3.4-alpha2+build1` versions
- Feature: compress level of tgz is now configurable via `CONAN_COMPRESSION_LEVEL` environment variable,
default 9. Reducing it can lead to faster compression times, at the expense of slightly bigger archives
- Feature: Add **powershell** support for virtualenv generator in Windows
- Feature: Improved `system_requirements()` raising errors when failing, retrying if not successful,
being able to execute in user space for local recipes
- Feature: new cmake helper macro `conan_target_link_libraries()`
- Feature: new cmake `CONAN_EXPORTED` variable, can be used in CMakeLists.txt to differentiate building
in the local conan cache as package and building in user space
- Fix: improving the caching of options from `conan install` in conaninfo.txt and precedence.
- Fix: conan definition of cmake output dirs has been disabled for `cmake_multi` generator
- Fix: `imports()` now uses environment variables at "conan install" (but not at "conan imports" yet)
- Fix: `conan_info()` method has been renamed to `package_id()`. Backward compatibility is maintained,
but it is strongly encouraged to use the new name.
- Fix: `conan_find_libraries` now use the NO_CMAKE_FIND_ROOT_PATH parameter for avoiding issue while cross-compiling
- Fix: disallowing duplicate URLs in remotes, better error management
- Fix: improved error message for wildcard uploads not matching any package
- Fix: remove deprecated `platform.linux_distribution()`, using new "distro" package
- Bugfix: fixed management of `VerifySSL` parameter for remotes
- Bugfix: fixed misdetection of compiler version in conanbuildinfo.cmake for apple-clang
- Bugfix: fixed trailing slash in remotes URLs producing crashes
- Refactor: A big refactor has been do to `options`. Nested options are no longer supported, and
`option.suboption` will be managed as a single string option.

This has been a huge release with contributors of 11 developers. Thanks very much to all of them!

- Bug Fix: Handling of transitive private dependencies in modern cmake targets
- Bug Fix: Missing quotes in CMake macro for modern cmake targets
- Bug Fix: Handling LINK_FLAGS in cmake modern targets
- Bug Fix: Environment variables no propagating to test project with test_package command