Fix 'make build_plt'

The dialyzer --add_to_plt call was not specifying the proper
rebar plt to add diameter to.
Merge pull request #355 from tuncer/fix-make_build_plt

Fix 'make build_plt'
Add {prefix, atom()} option for abnfc_opts

Specify the atom to use as a prefix for the decoder and generator
functions inside the parser's module.  Default is ''.
Add {parser, module()} option for abnfc_opts

Specify the module to use for parsing the ABNF grammars.  Default is
'abnfc_rfc4234'.
Add {qc, proplist()} option for abnfc_opts

Specify the options to use for the generator functions inside the
parser's module.  Default is [].