Minor changes to shader repr()
Nicer buffer-type error reporting
Merge branch 'master' of github.com:vispy/vispy
Further modified shader repr() to support description lines that occur past the first line,
delayed descriotion generation until repr is called.
Merge branch 'master' of github.com:vispy/vispy
Merge branch 'master' of github.com:vispy/vispy
Added beginning of line visual.

* Collection of transform shaders (only STTransform is implemented)
* Ability to specify color as uniform, RGB attribute, or RGBA attribute;
  the shader handles this by attaching the appropriate input shader
* Ability to attach custom transformation shaders
* Shaders get _on_enabling callbacks so they may specify uniforms/attributes