Initial line number reporting
Made line number reporting optional via config.h
Homing and feed hold bug fixes.

WARNING: Bugs may still exist. This branch is a work in progress and
will be pushed to the edge branch when at beta stability. Use at your
own risk.

- Homing freezing issue fixed. Had to do with the cycle stop flag being
set incorrectly after the homing cycles and before the pull-off
maneuver. Now resets the stepper motors before this can happen.

- Fixed an issue with a rare feed hold failure. Had to do with feed
hold ending exactly at the end of a block. The runtime protocol now
sets the QUEUED and IDLE states appropriately when this occurs. Still
need to clean this code up however, as it’s patched rather than written
well.

- Updated version build via $I command.

- Forgot to comment on a new feature for the last commit. Since steps
are integers and millimeters traveled are floats, the old step segment
generator ignored the step fraction differences in generating the
segment velocities. Didn’t see like it would be much of a big deal, but
there were instances that this would be a problem, especially for very
slow feed rates. The stepper algorithm now micro-adjusts the segment
velocities based on the step fractions not executed from the previous
segment. This ensures that Grbl generates the velocity profiles EXACTLY
and noticeably improves overall acceleration performance.
Merge commit 'cd71a90ce8a770e0030ed6c9bac805b89724e275' into dev

Conflicts:
	limits.c
	motion_control.c
	report.c
Commenting updates. Minor bug fix with exit of soft limit event.
Merge pull request #356 from robgrz/dev

Line number reporting as compile-time option.
Minor updates to line number feature.

- Changed line number integer types from unsigned to signed int32.
G-code mandates values cannot exceed 99999. Negative values can be used
to indicate certain modes.

- Homing cycle line number changed to -1, as an indicator.

- Fixed a reporting define for the spindle states that was broken by
the last merge.
Minimal probing cycle working.  Supports both G38.2 for error and G38.3 when no errors are desired.
Added grbl planner Matlab simulator for test reference. Updated line number compile-time option.

- Added a grbl planner simulation tool that was written in Matlab and
Python. It was used to visualize the inner workings of the planner as a
program is streamed to it. The simulation assumes that the planner
buffer is empty, then filled, and kept filled. This is mainly for users
to see how the planner works.

- Updated some of the compile-time ifdefs when enabling line numbers.
The leaving the un-used line numbers in the function calls eats a
non-neglible amount of flash memory. So the new if-defs remove them.
Merge pull request #362 from robgrz/dev

Minimal probing cycle working.  Supports both G38.2 for error and G38.3 ...
Probe cycle line numbers ifdef fixes to get it to compile.

- Updated some of the ifdefs when disabling line numbers feature.
Getting messy with this compile-time option. This will likely get
cleaned up later.

- This is just a push to get the new probing code to compile. Testing
and optimization of the code will soon follow and be pushed next.
G38.2 probe feature rough draft installed. Working but needs testing.

- G38.2 straight probe now supported. Rough draft. May be tweaked more
as testing ramps up.

- G38.2 requires at least one axis word. Multiple axis words work too.
When commanded, the probe cycle will move at the last ‘F’ feed rate
specified in a straight line.

- During a probe cycle: If the probe pin goes low (normal high), Grbl
will record that immediate position and engage a feed hold. Meaning
that the CNC machine will move a little past the probe switch point, so
keep federates low to stop sooner. Once stopped, Grbl will issue a move
to go back to the recorded probe trigger point.

- During a probe cycle: If the probe switch does not engage by the time
the machine has traveled to its target coordinates, Grbl will issue an
ALARM and the user will be forced to reset Grbl. (Currently G38.3 probe
without error isn’t supported, but would be easy to implement later.)

- After a successful probe, Grbl will send a feedback message
containing the recorded probe coordinates in the machine coordinate
system. This is as the g-code standard on probe parameters specifies.

- The recorded probe parameters are retained in Grbl memory and can be
viewed with the ‘$#’ print parameters command. Upon a power-cycle, not
a soft-reset, Grbl will re-zero these values.

- Moved ‘$#’ command to require IDLE or ALARM mode, because it accesses
EEPROM to fetch the coordinate system offsets.

- Updated the Grbl version to v0.9d.

- The probe cycle is subject to change upon testing or user-feedback.
Probing command gets stuck in hold if several g38.2 are submitted
Ex.
G0 X0 Y0 Z0
G38.2 Z-10 F100
G10 L20 P0 Z0
G0 Z2
G38.2 Z-1 F50
G10 L20 P0 Z0
G0 Z2
G0 X0 Y0
G38.2 Z-1 F100
G0 Z2
Merge pull request #368 from henols/dev

Probing command gets stuck in hold if several g38.2 are submitted
Probing command gets stuck in hold if several g38.2 are submitted
Ex.
G0 X0 Y0 Z0
G38.2 Z-10 F100
G10 L20 P0 Z0
G0 Z2
G38.2 Z-1 F50
G10 L20 P0 Z0
G0 Z2
G0 X0 Y0
G38.2 Z-1 F100
G0 Z2
Added Probing to Mega2560 and fixed Shapeoko2 compile error
Merge pull request #373 from EliteEng/dev

Added Probing to Mega2560 and fixed Shapeoko2 compile error
Comment corrections and function call update.
Merge pull request #3 from grbl/dev

Update Dev from official grbl