This code worked before because of bug in qualifiied package protection
implementation in DMD which resulted in merging protection levels of
aggregates and their member symbols.
The docs and API still stay in one file.
With time and refactoring more internals may be
exposed such as parser, each engine explicitly
and the sample generator (generator.d).
Also inclusdes changes prompted by reviews/pulls:
Convert spaces-->tabs in makefiles.
Move things (again) to std/regex/internal.
Use new package(std.regex) feature.
Remove C-style arrays (some other pull against regex.d).
