Added fov type and test

Toggling works in the test, more tests might be required.
fov_y is now used internally for rendering.
Since fov_y is updated when fov is set, which is updated when fov_type is set, I had to explicitly set fov_type to the default (horizontal) outside of variable declaration, I've done it in _merge_options now.
Might be a thing to look at if it shouldn't be done that way.