Usart unification

Join the interfaces for Usart polling and interruptive.

Tutorial of use

Readme is updated for user.

One fix on usart

Fix a continuous reset problem in usart driver when running on interruptive.

Memory map is segregated.

Memory map is segregated. In order to manage each device easier.

Before a big change

In the next revisions there will be significant large changes in the project, so we are tagging the current-state.

Initial version

Initial version, with a simple functional example.