* Allow to parse four element vectors
* Allow colors defined in HTML notation (#rrggbbaa)
in CEL scripts
* Refactor Overlay::Rectangle to an independent class
* Refactor CelestiaCore::OverlayImage to an independent class
* Refactor CelestiaCore::View to an independent class
* Rename Renderer::getScreenSize to getViewport
* Add wrappers for scissors test and MSAA control
Added LogSize option to celestia.cfg. The value of LogSize controls the number of rows in Celestia's console log. Added comment and usage example to celestia.cfg.