Get things in shape finally:

  * Move the Forward code into its own module.

  * Separate out the excluded MX filtering magic.

  * Write tons of tests for the MX filtering.

  * Normalize every name used in a comparison.

  * Use Data.Map and Data.Set for MX filtering.

  * Update some documentation.

  * Update the ghci file with new modules.

  * Add the Forward module to the cabal file.

  * Make sure no spurious newlines are output.

  * Update the TODO.