Implementation Plan for Windows Resource Files (#142)

RC scripts are quite common for Win32 application development. It'd be nice if Cabal were able to compile and link resource scripts at build time. Since `windres.exe` comes with mingw-w64, all that's needed is to teach cabal how to use it generate object files from RC files. I'd like to propose the following:

- Addition of an `rc-sources` field to the cabal file spec, functioning just like `c-sources`, `asm-sources`, etc.
- Addition of an `rc-options` (or perhaps `windres-options`) field to the cabal file spec, functioning just like `cc-options`, etc.
- Have cabal call `windres.exe` on all of the `rc-sources` with the `rc-options`, respecting the `includes` and `include-dirs` fields, and the `--extra-include-dirs` flag.
- Have cabal include the resulting object files when linking, just like object files generated from `c-sources`.

If this is a reasonable path forward, I'd be happy to tackle the implementation.

Start by reading Cabal's existing handling of c-sources and asm-sources, including how fields, options, include paths, and generated object files are processed. Define the resource-file fields and windres.exe integration there; done means RC sources compile with the requested options and include paths and their objects participate in linking.

Written by the indexing model from the issue text.