Renamed TEENSY_3 to PJRC_TEENSY_3

Updated the demo Makefile and readme to reflect this.

Signed-off-by: JCube001 <jacobm117@gmail.com>
Setup demo makefile

Signed-off-by: JCube001 <jacobm117@gmail.com>
Began to setup hal

Signed-off-by: JCube001 <jacobm117@gmail.com>