Arc error-checking update.

- Updated offset-mode arc error-checking to EMC2’s version: The old
NIST definition required the radii to the current location and target
location to differ no more than 0.002mm. This proved to be problematic
and probably why LinuxCNC(EMC2) updated it to be 0.005mm AND 0.1%
radius OR 0.5mm.
Fixed atomic access to flags in sys.execute.

This seems to fix the bug that caused Grbl to hang during some operations,
especially jogging.
Minor bug fixes and updates. Line number tracking.

- Line number tracking was getting truncated at 255, since it was using
wrong variable type. Fixed it with a trunc().

- Increased the max number line allowed by Grbl to 9999999 from the
g-code standard 99999. The latter seems to be an arbitrary number, so
we are allowing larger ones for at least one known use case scenario.

- Created a new test directory to contain some testing g-code to proof
the firmware. Only got started with one test case so far. More will be
inserted as needed.

- Some other commenting updates to clarify certain aspects of the code.
G-code parser G0/G1 bug fix.

- Although stated as invalid in the NIST g-code standard, most g-code
parsers, including linuxcnc, allow G0 and G1 to be commanded without
axis words present. For example, something like ‘G1 F100.0’ to preset
the motion mode and feed rate without a motion commanded. Older CNC
controllers actually required this for feed rate settings. This update
should now allow this type of behavior.
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
Realtime rate reporting. Updated decimal places.

- Added a new optional compile-time feature for ‘realtime’ (within
50ms) feed rate reporting. When querying for a status report, a new
data value will state the current operating rate. It’s only beta at the
moment and has some kinks to work out.

- Updated the code for printing floating point values to N decimal
places. Generalized the main floating point print code to accept a new
decimal places value and created a set of handler functions to print
certain floating point value types used in Grbl, like position, rates,
coordinate offsets, etc. All of these have different decimal
requirements and change when printed in mm or inches mode.

- Number of decimal places for the different value types can be
re-defined in config.h, but there shouldn’t be a need for this, as
these are physically limited.

- Removed the decimal places settings, as this was now obsoleted by the
new decimal places code.

- The new decimal places code also saves almost 300kB in flash space,
as it’s more efficient.
minor tweaks for mingw.
Don't need kbhit.h
Update readme.md
formatting
New G43.1/G49 gcodes. Not working yet!!

- Pushed this uncompleted code to merge a conflicting pull request.

- New G43.1 and G49 g-codes to be installed. The beginnings of it are
in place. These g-codes are intended to be used in conjunction with
probing and allow GUIs to set tool length offsets without Grbl needing
to store a tool table.

- G43.1 is defined as a dynamic tool length offset that is not stored
in memory. Rather, when commanded, these are applied to the work
coordinates until a reset or disabled by G49. This works much like G92.
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
G43.1/G49 tool length offset installed. Minor bug fix.

- Minor bug fix that caused G92.1 not to work. The mantissa of G92.1
was not computed correctly due to floating point round-off errors and
the use of trunc(). Fixed it by changing the computation with round().

- Installed tool length offsets with G43.1 and G49! True tool length
offsets via G43 are not supported, because these require us to store
tool data that we don’t have space for. But we’ve come up with a good
solution for users that need this. Instead we are strictly using the
dynamic version G43.1 via linuxcnc.org. Visit their website for more
details on the command.

- G43.1 operates by requiring an axis word and value to offset the
configured tool length axis, which can be configured for any axis
(default Z-axis) in config.h. For example, ```G43.1 Z0.5``` will offset
the work coordinates from Z0.0 to Z-0.5.

- G49 will cancel the last tool length offset value and reset it to
zero.

- Tweaked the ‘$#’ parameters report. `Probe` is now `PRB` and a new
value `TLO` states the tool length offset value.
Syntax fix for gcode.c

- Whoops! Missed a bracket and it wasn’t compiling. Now fixed.

- Updated the unsupported gcodes listed at the end of the gcode.c file.
Merge pull request #436 from kfoltman/dev

Fixed atomic access to flags in sys.execute.
Isolate atomic bit flag for execution.

- Denoted bit_true_atomic only for sys.execute bit settings. All other
bit_true type calls are for local variables only and don’t need atomic
access. Still looking into other ways of setting these flags without
requiring atomic access, but this is a patch for now.
Version and build update.

- Incremented from v0.9e to v0.9f due to the new g-codes, velocity
reporting option, decimal printing refactoring, grbl-sim updates, and
G0/G1 bug fix.

- Settings version was also incremented since settings.decimal_places
is now gone.
Merge remote-tracking branch 'origin/dev' into dev

Conflicts:
	config.h
	coolant_control.c
	gcode.c
	gcode.h
	limits.c
	motion_control.c
	nuts_bolts.h
	print.c
	print.h
	probe.c
	protocol.c
	report.c
	report.h
	serial.c
	settings.h
	sim/.gitignore
	sim/Makefile
	sim/README.md
	sim/avr/interrupt.c
	sim/avr/interrupt.h
	sim/avr/io.h
	sim/config.h
	sim/eeprom.c
	sim/main.c
	sim/planner_inject_accessors.c
	sim/serial.c
	sim/simulator.c
	sim/simulator.h
	spindle_control.c
	system.c