Working PRU assembly demo

Ultra basic C + PASM code demonstrating communication via
memory mapping.
Added device-tree overlay files, improved docs.
Stupid script is less stupid.
Working GPIO toggle and input demo using memory mapping.
Added macros and header file.
Deleted example files.
Reverted back to RAM addressing (need to use a single pin as I/O).
Revert "Reverted back to RAM addressing (need to use a single pin as I/O)."

This reverts commit bb80d23a8016da7602f88a47e421a4770f1eaa30.
Progress in RAM-based sensor usage
This should work but it doesn't, so... yeah.
Added folder for PRU serial work.
Proof-of-concept for PRU serial communication.
Created read macro. Read 4 bytes at a time in a loop now.
Read/write 4-byte values with proper output.
Confirmed test map algorithms work
Added arduino version of serial test. Working. Yay.
Using 8 bit integer values instead of strings.
Merge remote-tracking branch 'origin/dev' into notification
Rewrote to use a sync/start pin and 16-bit values.
Notification testing for LED