Math: Added Vector2::cross().
Mention support of both `glibc` and `newlib` NaCl toolchains.
Doc++
Primitives: added 2D/3D Line primitive.

No shit. This is usable mainly if some common code expects the
mesh wrapped in MeshData and thus it is better to just have this tiny
class instead of doing it manually.
DebugTools: 2D and 3D LineSegment support in ShapeRenderer.
Clang compilation fixes.