Added more "OpenFail" errors to help users

So they know better if another app is locking their serial port.
Added EOF check to not close port prematurely
Merge pull request #3 from jarretluft/master

GRBL BufferFlow Algorithm
Version 1.6
Update README.md
version 1.6 binaries
There's another check for EOF which needs to be enclosed inside the number of characters read check...
Merge pull request #4 from mandrav/master

An EOF check has slipped...
Update README.md