Mobile diff viewer, allows for a top-down rendering of diff fragments which is
friendlier for mobile devices. Contains a bunch of CSS stylings only to be
applied when screensize <= 720px, most of which aim to eliminate wasted space.
Top-down view is acheieved by adding a context variable
diff_file_fragment.html, which will render diff lines using a different
printf-formmated template (
mobile_line_fmt). The context variable also
diff_lines tag to perform additional formatting of data
it receives before passing it to the template.