Another major update

Added support for animated images (in the form of image strips), which
fixes #106. Added an index system for Pokémon, which fixes #91. Added a
sound system, including Pokémon cries, which fixes #107. Added the
ability to have special lighting overlays for different scenes, such as
a darker overlay for nighttime scenes. Incorporated Sprite(s) into
File. Added the `~>` notation into `_()`. Fixed an issue with
BattleServer and Client. Health is now properly stored by Pokémon.
Improved File.js

Files can now have fallbacks, and error functions if none of the files
could be loaded. This fixes #105.