speed up distance()

  - use BigInt method calls rather than overloading.
  - make fewer calls to badd().
  - access the k hash through one less level of indirection.
  - use implicit $_ where possible.
Merge branch 'master' of https://github.com/JRaspass/perl-Acme-KeyboardMarathon into JRaspass-master

Conflicts:
	lib/Acme/KeyboardMarathon.pm
Patch from James Raspass <jraspass@gmail.com> that vastly improves speed.
Merge branch 'JRaspass-master'
Merge branch 'master' of https://git.crescendo.net/perl-Acme-KeyboardMarathon