vdb_tool

[kmuseth]

Signed-off-by: Ken [email protected]

This branch replaces #1317, which has a signoff issue

A new command-line tool, dubbed vdb_tool, that can combine any sequence of the of high-level tools available in openvdb. For instance, it can convert a sequence of polygon meshes and particles to level sets, and perform a large number of operations on these level set surfaces. It can also generate adaptive polygon meshes from level sets, render images and write particles, meshes or VDBs to disk or stream VDBs to stdout so other tools can render them (using pipelining).