Custom model files can be uploaded by the user from an additional
menu bar item. They will appear in the dropdown model selection list and
can be selected like any other model. Once the user refreshes the page
the user provided models will no longer be available.
This pull also includes josepharhar's build.js, package.json, gitignore, and
README changes. It made it much easier to work with this project since the
generated JS files don't need to be manually modified and it is easier to build
the project by simply running `npm install` then `npm start`.
If he likes I can remove those changes from this pull and he can submit them
seperately.
Working with

Vec4 parse code was broken. Fixed now. Added some syntax error messages for uniform assignment.

Users can upload custom textures to apply to their models. They can also
add custom Uniform variables that are float, int, bools, vec2, vec3, vec4,
or sampler2d.
After a texture is uploaded it can be accessed by specifying the filename in
the uniforms tab. In the default text for Uniform there is a default texture
specified as `sampler2D my_texture = "textures/beanie.jpg";`
There is a new snippet showing how to apply a texture that is available
in the Uniforms tab.
The uniforms tab now highlights parsing errors.