Fixed mushrooms being horizontally flipped

How the heck did that escape notice for so long? I'm honestly
embarrassed.
Fixed crouch jumping & sliding

Also added in mario.keys.left/right_down, as recommended by brycepauken
Fixed exit point of Underworld in 8-1
Merge pull request #49 from sirctseb/master

Fixed exit point of Underworld in 8-1
Fixed Mario dropping through floor when hit

(hopefully)
Stars may no longer be hit by fireballs
Editor.js typo: "editorPeventClicks"
Fix mario not reversing direction after some skids

To replicate original bug: Make mario skid (eg. have mario run in
one direction, and then try running in the other direction to start
skidding). While skidding, release and (quickly) repress the shift
button. On most skids (particularly the longer ones), Mario will
fail to begin running in the other direction once the skid is complete.
Merge remote-tracking branch 'upstream/master'
Actually fixed editor(.js) scrolling
Merge remote-tracking branch 'upstream/master'
Merge pull request #62 from brycepauken/master

Fix mario not reversing direction after some skids
Changed fireball sound when hitting solid objects

Changed the fireball sound so that it plays Kick.wav when hitting enemies, and Bump.wav when hitting solid objects.
Restore end level fireworks

Fixes a couple of issues that were preventing the fireworks from appearing at the end of the level
Prevent jumping noises while going through pipe
Merge pull request #68 from dwilhelmi/master

Changed fireball sound when hitting solid objects, fixed fireworks, fixed jumping noises while going through pipe.
Platform-independent sounds

Both .mp3 and .ogg files are included, so all major browsers should be
able to play all audio.
window.controls as a Controls object added

CTRL also works for sprint/fire now, because nobody can disable sticky
keys.
"Starman" -> "Star"
Removed .mp3 from "Game Over" sound