Add an overview page for Drawing in GameMaker

[YYBartT]

The current manual page on Drawing is limited in explaining how GameMaker's drawing works and mostly contains links to other pages that have more info and a function reference of specific topics.

It could be interesting to have an overview of drawing in GameMaker, similar to the Audio page, which gradually introduces the subject of audio and links to the relevant topics. Drawing is a much more extensive subject. An overview page could be useful, however.

Detail the structure of this page further and add the new page under the Additional Information section of the manual.