running grbl-sim.exe uses an entire core

[flynneva]

looks like there might be a memory leak or something somewhere.
i dont think this simulation should use an entire core.

OS: Ubuntu 20.04
Hardware: Dell XPS 13 laptop, Intel 7i7, 4cores, 8GB RAM

[flynneva]

this causes the sim to miss gcode commands - especially when trying to send an entire nc file.