Total rework of simulator for dev branch.  Create separate thread for interrupt processes.  Tick-accurate simulation of timers.  Non-blocking character input for running in realtime mode. Decouple hardware sim from grbl code as much as possible. Expanded command line options. Provisions for cross-platform solution.
reduce diffs with dev branch
minor tweaks for mingw.
Don't need kbhit.h
Update readme.md
formatting
Merge grbl-sim updates for v0.9.

- Removed some conflicting code in the main Grbl firmware source.

- Temporary patch for coolant and spindle control with streaming
applied.
Merge branch 'ashelly-sim-update' into dev