make sure character classes are tested in lookbehind
Fix backtracking, move out common code to ir.d
Mostly non-decoding Thompson matcher

Along the way do a major cleanup, sizably reducing total source code.

Kickstart engine is temporarily disabled.
Turn on kickstart for Thompson engine
Do less work in Thompson's quickTest

As we know ahead of time if there is input,
and the kind of it.
Kill tries in favor of matchers.

Everything is hooked to matchers by now and
generating tries just wastes time and memory.
Reuse matchers for identical character classes

Should help a lot with ctRegex memory consumption,
and slightly improve speed because of smaller memory footprint,
fitting better into CPU's cache.