Use embedded-hal traits

[kunerd]

To make this lib easier to (re-)use, it should make usage of the traits provided by the embedded-hal crate. The current impls in the hal module are already very similar to them, so porting should not be a big problem.

The only thing that needs clarification is whether to use the single pin or the port wise traits?

[kunerd]

First try using the new Delay trait from embedded-hal:

https://github.com/kunerd/f3-discovery-hd44780