TODO:

* implement snprintf with newSVpvf for >= 5.004, which is safer?

* add support for my_vsnprintf?

* try to perform some core consistency checks:

  - check if 'd' flag in embed.fnc matches with
    supplied documentation

  - check if all public API is documented

* check (during make regen?) if MAX_PERL in PPPort_pm.PL
  needs to be updated

* see if we can implement sv_catpvf() for < 5.004

* MULTICALL ?

* improve apicheck (things like utf8_mg_pos_init() are
  not currently checked)

* more documentation, more tests

* Resolve dependencies in Makefile.PL and remind of
  running 'make regen'