PixelCNC v1.11a - Improved image meshing, invert image, ...

A new PixelCNC version has been released.  From changes.txt:

 v1.11a

 - changed project mesh generation parms to better handle images that are larger or more varied
 - increased allowable number of subdivision mesh triangles
 - increased allowable number of render mesh vertices
 - fixed oversized image downscaling not working properly in metric projects
 - re-enabled debug mode for increased verbosity in log files (for debugging end-user bugs)
 - added error messagebox end-users can report about if problems are encountered
 - fixed stipple operation advection not scaling offset vectors per project measure units
 - increased 3D view camera zoom/dolly range
 - added 'invert image' option to swap black/white depth interpretation
 - fixed negative-value string editing logic
 - fixed excessively tiny spiral toolpath angle increment in metric mode