Engine Restructured

• Pluggable interface

• • engine is now abstracted with a usable interface. We can now plug in other engines....
  • use re::engine::PCRE;
  • use re 'debug'; is now lexically scoped, as is the use of any other engine.
  • default engine can be extended or instrumented post release without requiring a full build.
  • All your regex engines are belong to us!