doc: Convert print statements to functions.
doc: Remove local copy of plot_directive.

We already depend on matplotlib.sphinxext.only_directives, which is
needed by plot_directive, but not used by us anywhere. So why not depend
on the thing we actually use, and drop an extra file.

I am aware this breaks the gallery, for the moment. This will be fixed
soon-ish.
doc: Add necessary wrapper divs around content.
tutorial: Migrate seismometer example to FDSN.
doc: Import all of bootstrap's layout.html.

We've already got most of it to get the wrapper div's in place, so I
figure we might as well use all of it. We don't need all the v2
compatibility stuff, so it's not as big as the original. Plus, this
saves us the duplicate CSS files.
doc: Clean up empty lines in template.
doc: Setup gallery plot themes with new directive.

This directive just wraps around matplotlib's plot directive, and adds
the target link and required Bootstrap classes.
doc: Disable hi-res images in the gallery.

They aren't used for anything here.
doc: Wrap citations in a list-table.

This allows the labels to be equally sized instead of being a bunch of
separate tables.
doc: Fix the citations list styling.

It seems to be impossible to get the class onto the reference label
using pure reST, so we have to modify the HTML after it's created.
doc: Fix some typos in index page.
doc: Add ChangeLog page.