Add support for latest svgpathtools version and GRBL

[dravac]

I remove the dependency of svgpathtools as git submodules. Now svgpathtools is imported as python library.

My CNC run GRBL with CNCjs, so I did some changes.

Change absolute to relative (remove G90.1 and replace by G91.1; Changes the absolute values of G2 and G3 to relative values).

G64 and G81 are not supported by GRBL:

All tests are ok and run with arduino, except those containing G81.