Split GHC(-API) into multiple packages

Current GHC-API is pretty monolithic and a lot of data is hidden in monads. I'd prefer to have cleanly separated packages for parser, module system, type-checker, optimizer, code generator, linker. E.g. Haddock would certainly only use the first two, maybe three, steps. Advanced editing features in an IDE would use only the first three steps. A compiler for a Haskell dialect might use only optimizer and code generator. The packages should have clean interfaces. E.g. it should be possible to enter a Text or String into the parser and get a ByteString containing code or a pointer to executable code in memory from the code generator, with no need to write temporary files.

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Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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