Bincrafters-conventions

* internal: update pip requirements
* fix: typo exit -> exists
* fix: OpenSSL update script shouldn't return true for EOL OpenSSL versions; this can cause the creation of empty commits
* add latest CCI reference updates

* update XCode images 11 -> 11.2
* add Clang 9 builds
* fetch up to 600 repositories from the GitHub api for the remote feature
* update Linux host image Xenial -> Bionic
* remove Clang 7 workaround; use `conanio/clang70` container for new jobs
* remove check for existing readme in the checks features
* delete Bincrafters and Conan Community author attributes
* remote feature: put CI skip tags in the long commit description
* remove standalone CLI feature to update only the readme
* update check for `tools.get()` to look if `conandata.yml` is used
* increase minimum Conan version to 1.18.0 as it is the first version which supports `user/channel` as optional
* fix jobs_update not returning explicit value, causing the remote feature to not push modified files
* add latest CCI reference updates

* remove 32-bit builds more reliable
* add `del self.settings.compiler.cppstd` after `del self.settings.compiler.libcxx`
* do not require the `author` attribute anymore
* add Apple Clang 11 build jobs
* remove Apple Clang 9.0 build jobs
* delete Python meta lines
* CCI adoption: Add newest recipes

* update more recipe references to their corresponding CCI versions
* remove 32-bit builds and MinGW builds from CI jobs
* introduces `bincrafters-conventions:no-new-compiler-versions` tag to prevent bincrafters-conventions from adding builds jobs for newer compiler versions; can be used when a project doesn't support newer compilers. This tag can be added anywhere at the beginning of a CI configuration file (not within build jobs or afterwards) (https://github.com/bincrafters/community/issues/933)
* introduces `bincrafters-conventions:preserve-build-job` tag to prevent bincrafters-conventions from removing a particular 32-bit or MinGW build job. This tag can be added at the end of any line of a build job (it can't be added in a new, dedicated line). It can not be used to prevent build jobs for obsolete compiler versions from getting removed

Bincrafters-conventions can update now Azure Pipelines YAML files

https://github.com/bincrafters/community/issues/932

Features
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