Modernize library

[bts]

Hi Adam,

Thanks for this library!

I needed to make some changes to Control.RateLimit for my own purposes (i.e. to take MonadIO m instead of IO actions), but had to bring things up-to-date first before I could do that.

The two major changes I made were to:

• remove the use of a datatype context on RateLimit a
• switch from Chan to TChan due to unGetChan and isEmptyChan now being deprecated (see http://ghc.haskell.org/trac/ghc/ticket/4154). This adds a dependency on stm.

Before making my own (MonadIO) changes, I also took the liberty to reformat the module to try to reflect more recent Galois code on GitHub (at least as far as I could gather :). The reformatting occurs in the last commit in this PR if you'd prefer to drop that change.

If you'd happen to be interested in a version of Control.RateLimit that deals in MonadIO m instead of IO (using monadIO), then let me know and I can open another PR.

Thanks, Brian

[acw]

Looks good to me. Thanks for the patch! I'll bump a version and upload it to Hackage shortly.