Add Pixal3D backend

[iki77]

Is your feature request related to a problem? Please describe.
There is no support for Pixal3D backend, which allows multi-view to 3d generation.

Describe the solution you'd like
A fork of trellis.cpp which Pixal3D based on, available https://github.com/raven38/pixal3d.cpp

Describe alternatives you've considered

Additional context