Support creating framework targets

[kylef]

Currently the Xcodeproj generated build configurations for framework targets on OS X differ quite a bit compared to Xcode 5. For example, the following are simply omitted from the Xcodeproj generated target's build configuration:

"FRAMEWORK_VERSION" => "A",
"WRAPPER_EXTENSION" => "framework",

We need to adjust what build settings we are setting and align them with Xcode, along with introducing support for iOS frameworks.

• OS X
• iOS

This is required to do CocoaPods/CocoaPods#2272.

[mrackwitz]

I have already begun to add the new settings and according specs, including support for iOS and OS X frameworks. But I would wait for the GM until finishing a pull-request.

[kylef]

@mrackwitz I did some work too :'(

[mrackwitz]

@kylef Oh, great! Didn't noticed.

[fabiopelosin]

@kylef how does your patch compares to the work done by @mrackwitz on #166?