[CHANGES]
- Big reshuffle to move most code into Future/PP.pm in order to
support an optional Future-XS distribution too
- Attempt to load Future::XS by preference if it is available
- Additional unit tests for cornercases of XS implementation
- Remember to provide the AWAIT_WAIT API method
- Migrated Future::Queue out into its own distribution
[BUGFIXES]
- Bugfixes and unit tests for convergents on pre-cancelled futures
(RT144459)