feat(gcoder): step length management when splitting curve

[nojhan]

• Previous segment_to_gcode was splitting every curve in 1000, which may overstep the feed rate on some machines on small curves. This implementation starts by searching for a number of splits honoring (when possible) a configurable minimal step length.
• The step_length parameter is passed through the call stack and the --step-length argument is added to the interface.
• The CLI is put under __main__guard.
• WARNING -> NOTE for default parameters.
• Adds a --precision argument managing gcoder.precision.

[SebKuzminsky]

Thank you for these features, they all look really useful and I want to merge them.

Unfortunately we both did some work in parallel, and now there's a merge conflict. Please rebase your branch on top of the current master branch. (I can help with this if you want.)

Also, your commit does many different things... It's very much preferable if each commit does only one thing, so that they can be discussed and understood separately. If possible, when you rebase, please split this big commit up into smaller logical commits.

Thanks!

[nojhan]

This should be done with this forced push.