Slap-dash first attempt to get some more parsers

This attempt brings up a fairly large number of issues:

1.     fromEnv :: String -> Either String a

   is too weak to use recursively, we need to keep a parser
   of some kind or another around

   maybe something simple like

       fromEnv :: Atto.Parser a

   is enough.

2. we should pick an appropriate input format for Word and Int types
   (probably hexadecimal, but it should be done correctly)

3. methods of roundtripping through the parser should be tested---
   we don't have a genuine printer module (that'd be useless here)
   so it's a little challenging to know how we're building the tests

4. Tuples rely on better recursivity in the parser