Improved scaling on Retina devices.

https://github.com/phoboslab/Ejecta/issues/252
Merge pull request #110 from aroth/dev

Improved scaling on Retina devices.
docs typo
retina scaling rework
another attempt at proper retina texture scaling
retina scaling fixed, thanks @aroth for testing
camera fix to center levels smaller than screen
game now handles images loaded after preloading phase, resize/refresh bug fix
bug fixes for recent changes
incorrect tile shape extraction bug fix (thanks @aroth for finding)
first pass on fix for #113
transitioner fade out fix
background map merge fix for #114
example typo noted in #112
initial fix for #115
more fixes for preloading noted in #112
more bug fixes for #112
code beautified
example code beautified
fix for #125 found by @Pattentrick