mkpasswd; allow passing a salt-generating coderef via opts hash

Needs tests & POD.

	modified:   lib/App/bmkpasswd.pm
POD for new mkpasswd syntax
add hash opts / salt generator tests
minor optimizations, POD tweaks
Merge branch 'salt-coderef'

* salt-coderef:
  minor optimizations, POD tweaks
  add hash opts / salt generator tests
  POD for new mkpasswd syntax
  mkpasswd; allow passing a salt-generating coderef via opts hash