given bindings with inputs

[grayflow]

some_grammar = "s = 'something' "
bindings = { 'a': 'hello'}

instead of
g = parsley.makeGrammar(some_grammar, bindings)
g("blabla").s()
we want:
g = parsley.makeGrammar(some_grammar, {})
g("blabla", bindings).s()

and, it's even better if we could support overriding(the same name given latter override the previous one)