Error Messages

A first crack at not terrible error messages. 

For example, 

    $ liquid tests/neg/Baz.hs

produces:

    tests/neg/Baz.hs:7:13-25: Error: Liquid Type Mismatch
      Required Type
        VV : Int | (VV < xana)
     
      Actual Type
        VV : Int | (VV == ?a) && (VV > xana)
     
      In Context
        ?a   : Int | (?a == (xana + ?b))
        ?b   : Int | (?b == (1  :  int))
        xana : Int
   
   
    tests/neg/Baz.hs:12:11-15: Error: Liquid Type Mismatch
      Required Type
        VV : Int | (VV < x)
     
      Actual Type
        VV : Int | (VV == (x + ?a))
     
      In Context
        ?a : Int | (?a == (1  :  int))
        x  : Int