Implement vertex color support for Wavefront Object (.obj) file format

[TresSims]

Description

Implementation of reading vertex colors for the Wavefront Object (.obj) file format using two common methods:

• inline with the point location in v x y z r g b format
• A method used by Z-Brush using a block of MRGB values in hexidecimal format

Implementation of writing vertex colors using v x y z r g b format.

Motivation

I've been working on some tools to validate .obj files that are exported from Houdini and Z-Brush that include vertex color, and needed to be able to read vertex color as exported by those programs.

Benefits

Vertex colors generated by many Digital Content Creation tools including Houdini and Z-Brush can now be read and processed in pmp-library

Drawbacks

There is no official support for vertex colors in the Wavefront Object file specification, so this is technically implementing features that is not a part of the official specification, however many modern computer graphics tools do read and write vertex colors for obj files in this way.