-ported to setup.py, works with pip also
-code has been moved around due to setup.py
-new entry-point cli tool 'rezolve', eventually existing cli's (rez-env,
 rez etc) will go thru this.
-changed rez-env and rex shell management somewhat, to move more towards
 shell independence.
-a lot of things will be broken in this branch atm - most cli's are missing,
 rez-build, rez-release will probably not work etc. This is coming.