Software serial implementation. Compile with SOFTSERIAL_19200_LOOPBACK to test. Without the define the implementation will have no effect. Next step is to add a 'feature' to enable softserial and settings for the baud rate. Note, only READ is currently supported, write will come later. The highlevel api calls are used in main.c. Uart implementation needs cleanup to make serial port code generic, see uart files for details.

git-svn-id: https://afrodevices.googlecode.com/svn/trunk/baseflight@390 7c89a4a9-59b9-e629-4cfe-3a2d53b20e61