Optimize `LIKE` pattern compilation

[dlurton]

At the moment it takes a pathologically large amount of time and RAM to compile large LIKE patterns.

#279 made the expression 'foo' like '%<n>%' (where '' is 1500 '!' characters) take ~2.6 seconds to compile which is down from ~37 seconds and a big improvement but this is still an order of magnitude too slow. This should take significantly less then that even--into the tens of milliseconds or even less.