Add USART Micro Python Bindings

* Add Micro Python bindings to usart.c
* Export USART python object to namespace pyb
Add DEBUG flag to Makefile

* Add a DEBUG flag to Makefile, enables: "-O0 -ggdb"
Fix Makefile typo
Merge pull request #127 from iabdalkader/master

Add USART Micro Python Bindings