Fix a bug where "goto(root, 255)" is not initialized properly.
Add interface ac_match2(). The difference between ac_match() and ac_match2() is that
the former returns a pair (the match-begin and match-end) encaptured in a structure,
however the later returns a single interger (match-begin).

The rationale for this change is that luajit is currently not able to JIT compile
Remove -flto from compile flags. It only degrades ahocorasick.so's performance.