WIP
-new virtualenv-based installer, install.py
-all bootstrapping removed
-bootstrapped rez package generation removed
-setup.py can still be used directly, installs rez as a normal python module.
In this case, cli tools are disabled inside a rez-env'd env
-finished up on venv-based installer
-added distlib - new commit which adds the interpreter_args
-using distlib to patch venv-generated rez cli binaries
-added rez ingestion of itself in rez-bind.
-added --subdir option to venv installer
-minor update to new install.py
-some cleanup wrt completion scripts
-version up
-fixed bug in new install process, not correctly recognising production install
-added support for {version} expansion in install.py install path
-simplified patched rez binaries - skips setuptools shennanigans
-fixed bug in bind modules incorrectly doing relative import of rez.py
-added pre/post commands
-fixed bug in install.py breaking _rez_fwd util
fixed bug in _rez_fwd, again
Merge branch 'pre_post_commands' into 2.0

Conflicts:
	src/rez/__init__.py
	src/rez/_sys/_setup.py
	src/rez/cli/env.py
	src/rez/resolved_context.py