Add new mbmesh program for producing 3D mesh files directly from a list of swath files

[MBARIMike]

Completion of the mbgrd2gltf program demonstrates successful conversion of single 2D bathymetry grid files into an efficient format for loading into any glTF capable tool, including javascript libraries and web browsers. I'd like to generalize and extend this capability by writing a program that takes similar inputs to the mbgrid program and produces 3D mesh files directly from the swath data. This bypasses the 2D gridding operation and would enable accurate representation of bathymetric features such as cliffs, spires, overhangs, and caves.

The targeted output file format is OGC 3D Tiles 1.1, whose fundamental tile format is .glb (glTF).

There are many resources available for writing a new mbmesh program:

1. The existing mbgrid code for reading a datalist of input swath data
2. The existing mbgrd2gltf code for writing Draco compressed glTF files
3. The documentation for Cesium/OGC 3D Tiles and the Cesium community forums for discussions amongst the developers and users
4. The ongoing development of 3D Tiles capability in X3DOM

The initial milestone for this development is the writing of a single root 3D Tile that can be opened in a web browser using X3DOM.