GitLab

* Add deprecated hs-source-dir

I replaced the note about `hs-source-dir` being deprecated in the
description of `hs-source-dirs` by a field of its own to include the
`deprecated` and `removed` fields because it's no longer in 3.0.

* Add note to hs-source-dirs about multiple components

Source directories can be shared among components but there's a
non-obvious caveat which I've tried to clarify with a note.

* Clarify shared source dir note

Modules in a shared source directory can inadvertently end up getting
compiled multiple times.

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