a start on std.regex conversion

few steps more
hacks on the way to integrate new uni into std.regex
workaround internal error
adjust Tries back to 2-level
another minor tweak, always use tries not sets for now
remove "optimization" that no longer helps
workaround compiler bug for now
MutltiArray is CTFE-able; corrections for workarounds in std.uni
refactor TrieBuilder
tweak algorithm to actually fast-track zero-pages