RELEASE 2.10.0: Misc Improvements

• The new expand_requires function has been improved (syntax such as foo-1+<1.* is supported); and a new '**' wildcard is added. See: https://github.com/nerdvegas/rez/wiki/Package-Definition-Guide#requirements-expansion
• Arbitrary functions, and variables with double leading underscore, are now stripped from installed packages (as well as python modules). This makes it more convenient to write programmatic package.py files. See: https://github.com/nerdvegas/rez/wiki/Package-Definition-Guide#package-attributes