Get working on ghc-7.7.20130908.

I make not guarantees about 7.8.

Changes:
* allow base 4.7
* add two type signatures that ghc couldn't infer
  (http://ghc.haskell.org/trac/ghc/ticket/5678)
* import annularWedge (I don't understand how this worked before)
Merge pull request #20 from joelburget/master

Get working on ghc-7.7.20130908.