Clean up, phase 0 - Githubissues

Various clean-ups and fixes:

Convert to Objective-C ARC
Upgrade to Xcode 7 settings
Format code per recommendations from Objective-Clean
Move 'main' code to its own file
Add .gitignore
Rename variables
Convert ivars to properties
Fix whitespace
and probably a couple of other things as well

What I'm really working toward is fixing #2, but this is the first step on the road of getting that working. I'm submitting this pull request now before the diff gets too large.

rharder / imagesnap

Clean up, phase 0 #12