Change sprite.hpp encoding from ISO-8859-1 to UTF-8 for consistency with other files
Make return stack directly available in mruby scripting interface
Add music from the forums to SMC.

Sources:
* http://www.secretmaryo.org/phpBB3/viewtopic.php?f=11&t=4082#p25639
* http://www.secretmaryo.org/phpBB3/viewtopic.php?f=11&t=5298#p32080
* http://www.secretmaryo.org/phpBB3/viewtopic.php?f=11&t=4113#p25976
Fix particle emitter’s vertical gravity not being saved.
Remove special image handling from static enemy.

They can just use cSprite’s default implementation.