Default features of the crate is now "stable". panic-halt is used as the
stable alternative.

The pin traits now take the channel as a type argument instead of an
associated type. This makes it possible for one type to be converted
into different channels. The output Pin type is now completely decided
by the implementing type. This allows `NoMatchPin` to work despite not
having a pin number.

All methods have been adjusted to take `&mut self` instead of `&self`,
since they actually mutate the state of the timer (e.g. `reset_timer`).

Examples have been updated to compile after the changes to constructors,
mutability and type arguments.