Properly handle meta-characters from Java regexes

[hyperpape]

There are a number of unsupported meta-characters that the standard Java regexes support. While I don't know if I'd support all of them, we should make sure that, for sake of avoiding confusion, it's not true that this library will parse them and give them a meaning different from what the standard library does.

Case in point:

backreferences: \1
quotation: \Q, \E
reluctant quantifiers: X??

possibly others.

[hyperpape]

The examples above and some others (reluctant and possessive quantifiers) are handled in

cadc2e9
8678a8b

I still need to review the whole syntax that Pattern supports and add to the documentation.