Move on to semver major.minor.patch and off -alpha

[yoshuawuyts]

This library hasn't seen any updates since June, and new libraries such as pin-project and pin-project-lite have since sprung up, rounding out the library space around pinning.

I'd like to propose we move off the -alpha prefix, and to a less volatile release channel, because -alpha versions will always be updated by Cargo which isn't great. In fact, I'd like to propose we move this library to semver major-minor-path so changes can be more accurately communicated, which seems desirable for a library that's underpinning (heh) the entire async ecosystem.

I hope this makes sense. Thanks!

[Nemo157]

See #26 moving to 0.1.0.

[cramertj]

Fixed in #26, releasing now.