Initial import

Initial import of source files.
Create README.md
Added levels

Now have levels.
Proper Levels

Add level ups and changing level background images. Centre text properly
Added sound effects

Flap sound for flying, squelch for collisions and a failure jingle for
game over.
Optimised images saving 14803 bytes / 28.6%
Restructure and minification
Merge branch 'master'