Fix podspec for coredata support

[ryanmaxwell]

I had to make the following adjustments to the podspec for this to integrate into my project (the new mantle 2.0 branch)

Basically, the 'GCC_PREPROCESSOR_DEFINITIONS' => "OVERCOAT_SUPPORT_COREDATA=1" doesn't work when cocoapods creates the umbrella header for the swift modules without paying attention to the preprocessor macro to include the header implementation. So i'm left with an incomplete module.

I moved the source files into subdirectories that better align with the subspecs.

I also removed the MTLManagedObjectAdapter.h from the Overcoat.h header as that should be pulled in by the consumers where appropriate (like Mantle.h is). I added MTLManagedObjectAdapter as a dependency for the CoreData subspec, and also updated the versioning requirements to the '~>' syntax which is a better way to specify non-breaking newer versions of a pod are supported.

I am not actively using the social support in Overcoat so I don't think i've fixed that integration.

[sodastsai]

I'll look into this later.

But one issue about the dependency is that I think it's better to keep both Mantle 1.x and 2.x supported, so this is why I wrote

ss.dependency 'Mantle', '<= 3.0'

instead of (in your PR)

ss.dependency 'Mantle', '~> 2.0'

And this is also why I didn't add MTLManagedObjectAdapter as default dependency.

TL;DR;
Any idea about to support only Mantle 2.x or both 1.x and 2.x?

[ryanmaxwell]

Oh sure, I didn't realize that you wanted to keep support for both, but that's a noble goal. There must be a way to set it up to work across all configurations and versions but I didn't have time to test all the possible configurations and just needed to get it compiling today :)

I'll try and look into it more when I get a chance