Created fadein and fadeout sequences
Refactored the fade methods

I combined Strip::sequence_fadein() and Strip::sequence_fadeout() into a
smarter (and smaller) Strip::fade() method that can do both. It can also
stop at any alpha point - it doesn't have to reach 0 or 255 opacity
like the previous methods.
Code cleanliness

Deleted some cruft files. Applied some commenting.