(README - minor improvement)

Ignore-this: 3365de93392857f67e7357181fe29596

darcs-hash:20130923165210-3a4db-56646c055fab27fba0c51b3ce7f60dc2816611ac
(add stuff from README to package-level docstring)

Ignore-this: 9bb9c7eea59351749ada5967a19e3672

darcs-hash:20130923165223-3a4db-0ba7241fd52e10653b2db074a5e21945aa458171
add example usage to README and package docstring (and add the snippets as doctests)

Ignore-this: 8b4d112a7414fb7459dacfd53a62d2d3

darcs-hash:20130923165447-3a4db-5c48a7d54e972edadeef2bb8ca147e4cb0d0c58f