Pex

* Support console scripts found in the PEX_PATH. (1265)
* Fix Requires metadata handling. (1262)
* Fix PEX file reproducibility. (1259)
* Fix venv script shebang rewriting. (1260)
* Introduce the repository PEX_TOOL. (1256)

This is a hotfix release that fixes `--venv` mode shebangs being too
long for some Linux environments.

* Guard against too long `--venv` mode shebangs. (1254)

This release primarily hardens Pex venvs fixing several bugs.

* Fix Pex isolation. (1250)
* Support pre-compiling a venv. (1246)
* Support venv relocation. (1247)
* Fix `--runtime-pex-root` leak in pex bootstrap. (1244)
* Support venvs that can outlive their base python. (1245)
* Harden Pex interpreter identification. (1248)
* The `pex` venv script handles entrypoints like PEX.
(1242)
* Ensure PEX files aren't symlinked in venv. (1240)
* Fix venv pex script for use with multiprocessing. (1238)

This release fixes another bug in `--venv` mode when PEX_PATH is
exported in the environment.

* Fix `--venv` mode to respect PEX_PATH. (1227)

1. Copy and paste the most recent CHANGES.rst section.
2. Adapt the syntax from RestructuredText to Markdown (e.g. remove RST links PR ... <...>`_``).

This is another hotfix release to fix incorrect resolve post-processing
failing otherwise correct resolves.

* Pex resolver fails to evaluate markers when post-processing resolves
to identify which dists satisfy direct requirements. (1196)