Simplify am/pm layer, move date layer to its own update method (so that it doesn't need to be checked each time)
De-initialize layers
Further improve 12 hour mode
Simplify battery percentage text
Added/changed comments and whitespace
Fix time update (apperently an app can only register one tick handler). Improved time_update code.
Merge pull request #6 from ad1217/master

Code cleanup and simplification