syntax tweaks, relax check, add set_pending(), deal with imported types

- allow trailing commas in list of resources

- make task.resources optional

- add rtfm::set_pending function which can be used to force an interrupt into
  the pending state. This is a replacement of the old rtfm::request.
  rtfm::set_pending takes the Interrupt enum provided by the device crate as
  argument. (The old rtfm::request took a task function as argument)

- the user may want to use types they imported into the root of the crate. These
  types are not available in e.g. `mod idle` so `idle::Resources` *can't* be
  defined in that module. To workaround this problem `idle::Resources` will be
  defined in the root, with some other name, and then be re-exported in the
  `idle` module.

- remove the "a resource only used by one task should be local data" check. In
  some cases you do want a resource owned by a single task instead of local
  data since `init` can access resources but not a task local data.