Housekeeping

- update some installation notes in README
- move clean/install into "Scripts"
- remove "Test"
- move some TODOs into a "TODO.md"
support for versioning autopkglib and MinimumVersion in recipe keys

- store AUTOPKG_VERSION in env so that it's available for reporting or other purposes (for recipes, metadata, etc.)
- currently version.plist contains a single value that would be manually incremented when new features added
  - would be good in the future to have another patch version that auto-increments with Git commits, ala munkitools
A couple last com.googlecode -> com.github

- in pkgserver launchd, URLDownloader