Log Message:
Update to 0.61, set LICENSE to public-domain (see below).

[Changes for 0.61]

* Added "=encoding utf8" to POD to fix author name display.
  No functional changes.

[Changes for 0.60]

* LICENSING CHANGE: This compilation and all individual files in it
  are now under the nullary CC0 1.0 Universal terms:

  To the extent possible under law, 唐鳳 has waived all copyright and
  related or neighboring rights to Module-Signature.

* Updated Module::Install to 0.91, prompted by Florian Ragwitz.