Allow setting local-doc-root in stack.yaml

[chris-martin]

Similarly to how we can specify local-bin-path, it would be great to also be able to customize local-doc-root to make the Haddock output always be generated in a predictable place. Right now I think I'm going to have to add a line to my Makefile to copy the output from $(stack path --local-doc-root) to where it needs to be. This is not terrible, I suppose, but doesn't seem like it should be necessary.

[iupii]

Why "component: options parsing" was removed? Looks like it should be there.