Fixed div. by zero error in max velocity calculation
TP: mostly fixed maxvel issue, traced to canon changes
Temporary revert from master to see if refactor is the case
Revert "Temporary revert from master to see if refactor is the case"

This reverts commit a0aabc78e01b3b76bc4b76c967dac9ff798fc2a5.
Troubleshooting canon

Reverted to 1-indexing, but this didn't solve the problem. It turns out
that XY rotation is to blame for choosing the wrong axis start / end
points, which had butchered the axis_len calculation. This current state
may not be right, but it runs on a few test programs so far.
Removed temp canon debug messages
Figure out the actual problem with canon / axis_len

Rotating the coordinate system is what broke the axis_len calculation,
and a stray rotation was present for the previous commits. The previous
solution doesn't work because rotation could be arbitrary.

This solution does work for any rotation, however. When calculating the
axis length for an arc:
1) calculate a 3D displacement from start to end in XYZ
2) unrotate the displacement vector in the XY plane (i.e. rotate by
-xy_rotation).
3) select the appropriate component by the active plane.
Merge branch 'hotfix/velocity-limits' into circular-blend-arc-rc3
docs are still generated even if explicitly disabled
xenomai-kernel is deprecated
Added missing test files for uneven axis vel
Corrected helical_length calculation bug introduced in canon refactor
Canon trailing whitespace cleanup
Fixed maxvel bug by correcting axis index for normal axis
Slight maxvel violations found still in line-line blending
this commit fixes #135
Fixed remaining maxvel violation due to incorrect angle in altitude calculation
Merge branch 'hotfix/tort-vel-violation' into circular-blend-arc-rc3
added M106 for fan control, commented out one echo line in M109
Merge pull request #137 from luminize/m106-command

added M106 for fan control, commented out one echo line in M109