Fix `drawCircle` signature in `PaintingWindow`.
Change signature of painting commands, update doc, hide functions using Qt objects.
Add unit tests for painting commands.
Fix wrong variable name.
Remove obsolete painting function.
Add a precision on the usage of DO_STATIC_ASSERT.
Merge branch 'fix-miscellaneous-compiler-warnings' of ssh://github.com/DO-CV/DO-CV into fix-miscellaneous-compiler-warnings