Merge pull request #6 from jarretluft/master

Changes to grbl buffer & Port Closing Fix by Jarret Luft. The ports weren't correctly closing on Raspi and Mac
v1.73

v1.73
Serial port fallback in windows

in case plug n play query fails it will fall back to just a com port
open technique of com1 thru com99. no friendly names this way.
v1.74
Remove registry call
v1.74
v1.74 binaries
Add mac binary
Merge pull request #10 from paulkaplan/mac-binary

Add v1.7.4 Mac binary
Update README.md
Update README.md
Added screenshots