Modify URL handling in LaTeX (partial fix for #55)

Specifically, we add the url package, as well as a small sed script to
rewrite any hrefs with identical link and text to be a \url instead. This
fixes the majority of the text-related hbox overruns described in #55

NOTE: the sed script is stupid and assumes that if the link text starts
with "http" then it's the same as the link destination.
Fix overflowing text in LaTeX PDF (partial fix for #55)

Various (mostly) minor edits to reduce the amount of LaTeX warnings about
overfull hboxes, incidentally making the PDF significantly more pretty.
Blanket scale down all images in LaTeX build (fix #55)

Most of the screenshots were too wide for the format (450px ~= 451 pts, when
the colums are 417 pts wide), so a simple inplace sed operation was added
to scale down every image by 8%, reducing the overfull hboxes by about as
much as can be expected.

Though there are still places where it overflows, the remaining places are
mostly sub-point overshoots or in a few cases, standalone lines with <5pts
overshoot. I.e. hardly noticable.
Merge pull request #58 from pettter/new_master

Fix most right-margin overflows (#55)