Pipx

- Add shell autocompletion. Also add `pipx completions` command to print instructions on how to add pipx completions to
your shell.
- Un-deprecate `ensurepath`. Use `userpath` internally instead of instructing users to run the `userpath` cli command.
- Improve detection of PIPX_BIN_DIR not being on PATH
- Improve error message when an existing symlink exists in PIPX_BIN_DIR and points to the wrong location
- Improve handling of unexpected files in PIPX_HOME (uranusjr)
- swap out of order logic in order to correctly recommend --include-deps (joshuarli)
- [dev] Migrate from tox to nox

- Do not raise bare exception if no binaries found (150)
- Update pipsi migration script

- Deprecate `ensurepath` command. Use `userpath append ~/.local/bin`
- Support redirects and proxies when downloading python files (i.e. `pipx run http://url/file.py`)
- Use tox for document generation and CI testing (CI tests are now functional rather than static tests on style and
formatting!)
- Use mkdocs for documentation
- Change default cache duration for `pipx run` from 2 to 14 days

- Fix upgrade-all and reinstall-all regression

- Add `runpip` command to run arbitrary pip commands in pipx-managed virtual environments
- Do not raise error when running `pipx install PACKAGE` and the package has already been installed by pipx (125). This
is the cause of the major version change from 0.12 to 0.13.
- Add `--skip` argument to `upgrade-all` and `reinstall-all` commands, to let the user skip particular packages

- Update logic in determining a package's binaries during installation. This removes spurious binaries from the
installation. (104)
- Improve compatibility with Debian distributions by using `shutil.which` instead of `distutils.spawn.find_executable`
(102)