Py-pip

- Fix "WindowsPath is not iterable" bug

- Add `--include-deps` argument to include binaries of dependent packages when installing with pipx. This improves
compatibility with packages that depend on other installed packages, such as `jupyter`.
- Speed up `pipx list` output (by running multiple processes in parallel) and by collecting all metadata in a single
subprocess call
- More aggressive cache directory removal when `--no-cache` is passed to `pipx run`
- [dev] Move inline text passed to subprocess calls to their own files to enable autoformatting, linting, unit testing

- Add support for PEP 582's `__pypackages__` (experimental). `pipx run BINARY` will first search in `__pypackages__` for
binary, then fallback to installing from PyPI. `pipx run --pypackages BINARY` will raise an error if the binary is not
found in `__pypackages__`.
- Fix regression when installing with `--editable` flag (93)
- [dev] improve unit tests

- Cache and reuse temporary Virtual Environments created with `pipx run` (61)
- Update binary discovery logic to find "scripts" like awscli (91)
- Forward `--pip-args` to the pip upgrade command (previously the args were forwarded to install/upgrade commands for
packages) (77)
- When using environment variable PIPX_HOME, Virtual Environments will now be created at `$PIPX_HOME/venvs` rather than
at `$PIPX_HOME`.
- [dev] refactor into multiple files, add more unit tests

- Fix parsing bug in pipx run

- list python2 as supported language so that pip installs with python2 will no longer install the pipx on PyPI from the
original pipx owner. Running pipx with python2 will fail, but at least it will not be as confusing as running the pipx
package from the original owner.