Houdini support

[AlexeySmolenchuk]

Added multiplatform CMake for Houdini with HDAs generation.

Generates ready-to-go release with this structure:

Everything seems to be working. The only issue is noisy Warnings of unknown "Notes" parameters.

Compilation is simple as this:

mkdir build
cd build
cmake ..
cmake --build . --target install --config Release

[mprater]

Thanks for this Alexey. I use the Notes parameter as a placeholder for general information about the shader, and as a place for users to make their own annotations about how they're using the plugin. Since the Notes parameter value is never used or accessed by the plugin, I don't include it in the pTable, but of course it is in the .args file. Do you think the warning has something to do with that? Katana doesn't complain about this and I don't use Houdini, so I'm not sure if this might be the issue or not.

[AlexeySmolenchuk]

I'm not sure if this might be the issue or not.

For testing/experimenting purposes it's fine.

[mprater]

I'm going to focus on the terminator issue first. CMake is not within my domain of expertise, so I'll need to have someone else take a look at this before I can consider pulling it. The other consideration is that the purpose of this repo is to provide the response functions themselves rather than a multi-platform build system to compile them. I only provided one at all so they could be easily tested and verified without too much effort. Since the responses need to be integrated into a aggregated set of surface responses to be of practical use, I'm not sure how beneficial building the plugins as they are really is.

[AlexeySmolenchuk]

Don't worry. Reject if you don't need it.

[mprater]

Alright, thanks Alexey. I really appreciate your interest. I'm going to leave this PR open for now, as I'd like to use it as an example to help me learn more about CMake.

Also, if you'd like to see these responses added to those that ship with RenderMan Lama, let Pixar know of your interest. I don't know if they've made a decision about that yet or not.

Thanks, mitch