Final tweaks

[benjeffery]

• [x] Remove rock-solid
• [x] fwdpy11 and rust examples
• [x] Grep for Todo
• [x] White background on blog images
• [x] Dangling commas on community
• [x] Twitter tags
• [x] Note "how to add a project to this page"

[jeromekelleher]

SGTM.

[benjeffery]

All these are done now. Twitter card seems to work, and can be tested by pasting a URL in the twitter compose box.