Offset for Face and Wire

[mkovaxx]

Splitting this off from #72 because Shape::offset_surface() is already implemented.

OCC has BRepOffsetAPI_MakeOffset for this.
Can work with either a Face or a Wire.
Supports 3 join types: arc, tangent, and intersection.
Has a "ToApprox" boolean setting to use only linear segments and circular arcs in the output.