Update ffmpeg.md

Add URL for core hosted on the buildbot and minor changes.

Update mkdocs.yml

Capitalization. Minor change.

Update core_template.md

Make directory section table based. Add height/width entries to geometry and timing section.

Move all images to the same parent directory. Update all uses of image syntax in all docs.

Issue Getting all the images in the same directory. #7 I went through each doc to make sure there's no major image breakage. Repo builds fine locally after this change.