Rework "Object Priority and Conflicts" section

[ISSOtm]

Fixes #12

Also added a link to a video (of mine, yes) and a NESDev thread showcasing examples of this happening with images.

[avivace]

Thanks Eldred. This looks like a very nice improvement overall. Re-clarifying the whole priority computing process is great.

My main issues here are over-stating and reinforcing concepts when really the manual-tone of the document should remain neutral. I've tried to fix all the occurences of this.

Also, for this kind of mechanism it may be worth to also aid the explanation with some simple flowcharts to introduce the general decision process implemented by the Game Boy, expanded by the details in the text (see #335).

[ISSOtm]

Applied and re-tweaked most suggested changes; they may be re-reviewed. A couple points are still to be discussed.

My main issues here are over-stating and reinforcing concepts when really the manual-tone of the document should remain neutral. I've tried to fix all the occurences of this.

Probably déformation professionnelle from gb-asm-tutorial, sorry about that :P

[ISSOtm]

Alright, this should be OK now