Mixing and matching V2 int and float types in the code creates too much
necessary work when an integer implementation has to interact with float
implementation. Let V2i create the cast for us and use floats for all
vector operations since they are mostly mathematic.
Some functions which should not be exposed in the API have been switched
to INTERNAL scope. We have a notion of an empty texture in World Traveller
that we can pass in situations where we just want to render a solid
colour with no associated texture.
The alternative to this was creating a separate shader for rendering
primitives but would require at some point to expose the AssetManager to
the renderer or the user on behalf has to manually switch shaders before
rendering (non-intuitive).
Separate notion of rendering a static string, i.e. for debug display that
is absolutely positioned, and rendering of a regular string that moves
with the game camera.
Rendering using a non-default quad specifies normalised coordinates
relative to the frame buffer size. Hence each render of these frames
should origin from (0,0) any other value is invalid.
