Add Podspec

Add a podspec to simplify the install process. The first time, the
developer will still have to make sure that the .lldbinit stuff is set
up, but subsequent times, enabling this functionality will be as simple
as including `pod 'LLDBQuickLook'` in their Podfile.
Merge pull request #1 from gfontenot/gf-cocoapods

Add Podspec