search.hpp has been enhanced to check nested_results if the default 'sub_match' and 'size_check' fails. This way we can test the nested bracket expressions.
I've removed the debug messages from regexp_grammar.hpp and the eval_seq metafunction class from the seq parser, which was an unnecessary transformation.
Another change is that the order of evaluation is forced now in build_seq and build_reg_exp.
Added 4 new test cases in the generated grammar.cpp with regress.txt: (foo), (?:foo), (?>foo)bar, foo(?=bar)