Pycam

* switch to Python3 (removing support for Python2)
* switch to GTK3 (from GTK2)
* switch OpenGL widget from GtkGLext to GLArea (part of GKT3)
* switch to new internal data handling
* enable loading and saving the workspace state (was disabled during v0.6.x)
* non-interactive batch processing allows scripted toolpath operations

* Fix import of DXF files with full-circle holes (github 112).
* Fix import of DXF files with bezier curves (github 116).
* Fix import of DXF with closed LWPOLYLINE.
* Fix line number reporting in CXFImporter.
* Fix python2/3 compatibility in CXFImporter.
* Better tests.

* Bounds: disable percent-based controls for zero-dimensions
* fix toolpath grid operation (issue 45)
* prevent negative bounding box dimensions
* additional dependency 'enum34' (only relevant for Python2)

* GCode: limit vertical feedrate (maximum speed of plunge move)
* removed experimental support for ODE
* the ODE library seems to be not actively developed anymore
* removed obsolete support for psyco
* prepared code for Python3
* Python2-only dependencies are still required
* updated help locations (from the old wiki to the new documentation website)

* greatly improved OpenGL visualization (contributed by Mattes)
* DXF importer:
* added bezier support for POLYLINE and LWPOLYLINE
* modularization of most features
* many more new features

* added extrusion for 2D models
* 2D projection of multi-layered 2D models
* significantly improved performance of 3D visualization
* fixed "help" links for Windows users
* added GTK theme with a native look&feel for Windows
* improved detection of library locations for Windows package
* added file type associations (mime) to the debian package
* minor bugs fixed