Advise people to use the unregister command instead.
POD edit.
Require latest pinto version.
Use fixed shebang.

Module::Build will convert this to a full path upon installation.
This makes it possible to use pinto even when switching perls with
perlbrew.  pinto will always use the same perl that you installed it
with.  Fixes thaljef/Pinto/#58.  Thanks @punter.