SUBST: Dynamicaly generate contexts

SUBST: Dynamicaly generate contexts

  - so far we needed to add contexts to subst.h + subst.c; Now we simply register new ones before registering tokens using them.
  - RegisterCTX is duplicate safe, so you can call it several times for the same context. That way you can make shure the context is there before registering handlers in several .c files.