Reorganize directories

[elalish]

This is one idea I had based on @fire's suggestion to reorganize our directories to make usage more clear. I want to make it more obvious what the core C++ library is with minimal dependencies, and separate all the extra stuff that's important, but optional. The idea is now we'd have two third_party folders, one for core dependencies and another for other dependencies. It also makes it more clear that meshIO is not a core part of the library, but really a support for test/debug.

I'd like to get some feedback on this before I go through and make it all build (and I might need some help with that @pca006132 🙏 ). Does this structure look like it'll be more clear and easier to depend on?

Wow, I was hoping Github would do a better job on the diff; that's pretty much unreadable. Okay, the change is to go from:

root/
|--- docs/
|--- collider/
|--- manifold/
|--- meshIO/
|--- polygon/
|--- samples/
|--- test/
|--- third_party/
|    |--- assimp/
|    |--- glm/
|    |--- google_test/
|    |--- graphlite/
|    |--- pybind11/
|    |--- thrust/
|--- tools/
|--- utilities/

to this:

root/
|--- docs/
|--- collider/
|--- manifold/
|--- polygon/
|--- third_party/
|    |--- glm/
|    |--- graphlite/
|    |--- thrust/
|--- utilities/
|--- extras/
|    |--- meshIO/
|    |--- samples/
|    |--- test/
|    |--- tools/
|    |--- third_party/
|    |    |--- assimp/
|    |    |--- google_test/
|    |    |--- pybind11/

[pca006132]

My two cents:

root/
|--- docs/
|--- examples/
|    | --- ...samples
|--- src/
|    |--- collider/
|    |--- manifold/
|    |--- polygon/
|    |--- utilities/
|--- test
|    |--- meshIO
|    |--- ...original tests, referencing examples
|--- extras
|    |--- ...tools
|--- third_party
|    |--- ...

The idea is to use a familiar structure, source files are grouped into src in root. I think we can just add a build instruction in the README to say that some third party dependencies are optional (test depends on assimp and google_test, python binding depends on pybind11).

[elalish]

Yes, I think I like that better. Still, I think I'd like to split up third_party to make it clearer what depends on what. I think people are more likely to understand our dependency graph from directory structure than by reading our README (though it should be there too). How about this:

root/
|--- docs/
|--- bindings/
|    |--- python/
|    |    |--- third_party/
|    |    |    |--- pybind11/
|    |--- wasm/
|--- examples/
|    |--- ...samples
|--- extras/
|    |--- ...tools
|--- src/
|    |--- collider/
|    |--- manifold/
|    |--- polygon/
|    |--- utilities/
|    |--- third_party/
|    |    |--- glm/
|    |    |--- graphlite/
|    |    |--- thrust/
|--- test/
|    |--- meshIO/
|    |--- ...original tests, referencing examples
|    |--- third_party/
|    |    |--- assimp/
|    |    |--- google_test/

[pca006132]

LGTM

[fire]

Looks good.

[elalish]

Thanks, closing in favor of #157.