Allow override of task names

[dansimau]

This allows overriding the task name using the name="" argument in @task, which in turn allows the use of Python-reserved words as task names without the need to create an alias eg.:

@task(name="import")
    def _import():
    [...]

[bitprophet]

This is getting the "maintainer needs this now" priority bump!

To do:

• Move the name kwarg to the end; having it at the start breaks backwards compat for anybody using positional args.
• Tests
• Docs
• Changelog

/me does this now.

[bitprophet]

All set.