make site more POSH

[btrem]

The markup relies on lots of divs where more semantic markup would be more appropriate:

• header instead of div.jumbotron
• figure instead of div.card
• etc.

Also, I don't think the bootstrap css is really necessary. For one thing, it's a pretty simple one page site. For another, modern css can do what bootstrap does, much more simply. Making these changes would provide a better example for anyone who views source of microformats.io, and would also resolve #29 (I think).

[btrem]

@gRegorLove I closed PR #60 because of the merge conflicts, and am starting over. But this time, I'm going to break up the work into smaller bits that you can more easily review, starting with #61.

More to come. I have done some work to normalize indentation and spacing of the source code (not the visible code examples), just to make it easier to work on the html.