Changed default type of Vector3 to float.
Implemented a few methods of RenderObject.

Implemented the constructor, destructor, `getVertexCount`, and
`toString` methods of RenderObject.
Added RenderObject's methods to the build system
Fixed a preprocessor error in RenderObject.hh.

The preprocessor was not correctly finding Vector3.hh, so I used relative
paths instead of include-path paths.