Optimized closestPointTo*() functions in GjkSimplex.

- Modified the test cases accordingly.
- Comments changed to reflect better math notations.
- Fixed doxygen comments.
- Changed unsigned int to size_t.
- Added scoped trace for the test cases.
Identified Vertices<VertexData>:: functions explicitly in TriangleMesh::farthestPointAlongDirection().

- Linux was giving error, while Windows compiled fine.