closes#69
this doesn't change functionality per se but improves diagnostics in some cases. Some hard errors
have becomes warnings, for example: when `resources` is empty, or when `idle.path` is set to the
default `idle` path.
- 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.
