new version of Lpeg

[roberto@... (Roberto Ierusalimschy)]

There is a new version of Lpeg available. Main changes:

- User-defined patterns in Lua.

- Several new captures (maybe too many...). Now we can not only
build syntax trees, but also perform generic semantic actions, do
substitutions (gsub), etc.

Now I think its main functionallity is in place. But I am considering a
few changes:

- Remove (or redesign) the "label" stuff. It does not mix well with the
rest of the capture mechanisms.

- Change the order of arguments to match (make it (pattern, subject)).
Then we can set a proper metatable and write patt:match(subject).

- Reduce the number of different captures (how??).

-- Roberto