fix ivory-quickcheck's QuickCheck constraint to == 2.6

later versions (2.7 and up) break API compatibility
c-syntax: initial commit.
reworked parser.
removed data generics stuff.
added comments parser.
push array indexes/derefs from expressions to statements.
wibble.
parser: change from monadic to applicative style.
statement parser: refactor into separate modules.
statement parser: use haskell token parser.
c stmts: parser wibbles.
stmt  parser: initial array assignments, loops work.
ivory-th: example wibbles.
parser: add binary, unary ops with C precedence.
loops: fix documentation.
AST: remove unused constructors.
c syntax: add remaining expressions.
parsers: refactor into separate modules.
parser: add function calls.
parser: finish stmts.
parser: major refactor, started type parser.