Fix bug preventing page scroll. Breaks marker pos.

This commit fixes a bug where you could only scroll the code view
element, not the whole page. This meant that you couldn't scroll the
page down past the GitHub header (if your page loaded in the default,
scrolled-to-the-beggining-of-the-page mode.)

HOWEVER, this also breaks marker positions. Because we no longer bound
the size of the code view element (and scroll the overflow,) the code
marker container matches the size of the code edit window, and so
marker layout is idempotent with code position; that is, the markers
are places on the page next to the line of code their marking. This
does us no good, since to see the shortcut to that line of code, we
need to... manually scroll to that line of code.

Working on fixing that.
Fix exceptions when run on non-code pages
Make scroll_to_lineno() more robust

It now works even if the page/elements dimensions change after adding
the marks, and even scrolls the line into view with a nice little
animation.
Remove unused rules from CSS
Display line marks in container fixed to viewport

This fixes the bug introduced in #09ece07df0 where line marks were
distributed over the length of the code blob container (and thus you
had to scroll to the line being marked to see the line marking.)

Now, the line markings container is sized to the browser window so that
it's possible to see all the marking in one window.

Further, when the code blob container fills the screen, the mark
container is fixed in place to the viewport (so it's always on screen
in the same place.) Otherwise (when, for example, we haven't scrolled
down so the code blob container fills the screen,) the code marks
container is at the top of the code blob container.
Version number bump
fix behavior when you scroll past bottom of code wrapper
fix naming, add debounce
rename didSetBorder
handle small files without scrollbars
Fix marker positioning for short files