Third-Party Library Support

Among other changes this release adds support for third-party libraries. cqparts was the first library integrated, which adds a layer on top of the CadQuery API to support parts and assemblies with constraints. See the change log for more details.

CQGI Release

This release adds support for the CadQuery Gateway Interface (CQGI), and moves the CadQuery library into a git submodule for better maintainability.