Adding a uiOrientation enum.

[simplexidev]

This enum would represent the orientation of control or other object, and could look like this:

_UI_ENUM(uiOrientation) {
    uiOrientationHorizontal,
    uiOrientationVertical,
};

This would remove the need of separate methods for creation of these controls. For example, in ui.h, both sets of creation methods for uiSeparator and uiBox could be turned into one method for each, both looking something like:

_UI_EXTERN uiBox uiNewBox(uiOrientation o);
_UI_EXTERN uiSeparator uiNewSeparator(uiOrientation o);