Refactor gamelets to use Lua packages

[tung]

gamelets.lua currently replicates part of the work done by Lua packages. Reworking gamelets to instead be loaded as packages would save some code, and collapse logic that would have to deal with gamelets and packages separately.

[tung]

Refactor gamelets. Closed by b86e9da.

• As the last package documented, this also Closed by b86e9da.
• New gamelet package is less than half the size of the old one.
• No more code duplication, Lua functionality duplication, redundant
  method names like 'get', needless abstraction over game.lua, and
  other general ugliness!
• Example gamelet code makes metatables public, which should help
  when using persist.lua.