Laserscad Versions Save

In this release:

• compatibilty and warning-free operation with OpenSCAD release 2019.05 (thanks to @jmgao)
• installation clarifications in the README

Years later, the copy & paste mistake in the readme is finally merged and released :partying_face: :see_no_evil:. Thanks to @hartzell for contributing.

This is a tiny feature release.

• Added lassert_version, a utility module for checking a model's required laserscad version.

This is a bugfix release for v0.2.0.

• Added more checks and messages:
  • make will terminate...
    • if laserscad.scad can't be found
    • if no lparts are defined
    • if duplicate lpart ids are used
  • lslice and lengrave now check all arguments for invalid values
  • more elaborate checks of lpart arguments
  • when calling make, any errors, warnings and echo statements unrelated to laserscad are printed
• SVG output by make engrave is now configurable (see readme):
  • unit can be specified
  • stroke width can be specified or disabled to fix problems with small/detailed shapes
• LGPLv3 license headers added to all files

• Added support for engravings (to identify lparts of just for show).
• Added support for slicing objects.
• Added support for models consisting of multiple scad files.
• Added more examples.
• The exporting procedure has changed significantly with this release. Details can be found in the readme.

All the features with basic functionality.