Merge pull request #10 from seltzered/master

minor: improve naming of osx-specific version of svgkit precompiled header; introduce osx support to podspec
There have been a few changes to the project layout since I forked it:
Source files that could be compiled on iOS and OS X were moved to a folder called "Shared additions".
The headers for the iOS vew classes got moved around, copied, and merged with their AppKit counterparts.
Point to the right branch (master) rather than the clean-up one.