lpeg v0.4

[roberto@... (Roberto Ierusalimschy)]

Yet another version of LPeg. The main novelty is a static check for
loops, both in repetitions and in grammars, that avoids the creation of
patterns with infinite loops.

Besides that, as announced, I removed the label option in captures and
changed the order of arguments to match. The metatable was already
set, so we can write patt:match(subject).

The implementation of captures also uses less memory (half, in some
relevant cases).

I hope it will be more stable from now on.

-- Roberto