Log Message:
Update to 2.500

Upstream changes:
2.500     2021-07-04 13:26:47-04:00 America/New_York
        - version bumped to account for change in fractional part precision

1.500     2021-06-20 20:30:24-04:00 America/New_York
        - adjust version number for bookkeeping reasons

1.300036  2021-06-17 09:51:12-04:00 America/New_York
        - add "maybestarttls" option, to allow opportunistic STARTTLS
          (thanks, Marc Bradshaw!)

1.300035  2020-10-10 12:34:29-04:00 America/New_York
        - drop some needless version checking from the days when we worked with
          broken Net::SMTPs (thanks, Bernhard Graf and Aristotle Pagaltzis and
          Pali Rohár)
        - documentation tweaks and spelling corrections (thanks, James E
          Keenan, Stefan Hornburg, M Somerville, and jazzkutya)