Add both foliage (all types: use Object.freeze() to create an enum) and branches to trees.  Add a foreach function to arrays (which takes optional start and end indices), used when translating foliages' vertices to the end of their branches.  Add gl-matrix.js to .gitignore (because it's the unoptimized version, and is hanging around for debugging illegal calls into its functions).  Move the view up by 10 units to be able to see into the branch parts of trees.  (Still todo: proper textures, and vines.)