Set gl version to 3.2, add a vertex array object.

Regarding VAO, from spec: "The default vertex array object (the name
zero) is also deprecated. Calling VertexAttribPointer when no buffer
object or no vertex array object is bound will generate an
INVALID_OPERATION error, as will calling any array drawing command when
no vertex array object is bound."
Merge pull request #8 from inmost-light/examples

Set gl version to 3.2, add a vertex array object.