Docsets for ReactiveCocoa

Hi,

I had some spare time, so I wrote a TomDoc to `<OtherDocumentationFormat>` converter, because I wanted a docset for ReactiveCocoa

I've added support for appledoc and Doxygen.
I haven't integrated it into the build process, because I'm not sure what your preferences are.

Appledoc
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Example docset here: http://dervishsoftware.s3.amazonaws.com/software/com.github.ReactiveCocoa.docset.xip

copy to `~/Library/Developer/Shared/Documentation/DocSets`

I made a couple of changes to appledoc to make it skip deprecated symbols, and to prevent it auto-linking to common English words (which are also RACSignal symbols)

An updated version of appledoc is here: https://github.com/antmd/appledoc

My pull request is: https://github.com/tomaz/appledoc/pull/397

You can use the 'brew' version of appledoc, but you'll get extra spurious hyperlinks in the output. The script to generate documentation checks for the presence of the extra command-line options.

Generate command-line:

	cd <ReactiveCocoaRoot>/ReactiveCocoaFramework/Scripts
	./generate_docs.sh -s ../ReactiveCocoa -x ../../README.md -f ReactiveCocoa -c GitHub -d com.github

Doxygen
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Doxygen output generates a folder 'html' in ~/Downloads

Generate command-line:

	cd <ReactiveCocoaRoot>/ReactiveCocoaFramework/Scripts
	./generate_docs.sh -s ../ReactiveCocoa -x ../../README.md -f ReactiveCocoa -c GitHub -d com.github

The doxygen output draws nice inheritance and collaboration diagrams.

Doxygen is supposed to be able to generate Apple DocSets, too, but I couldn't get it to work properly. I think it's a known issue.