Markdown section margin fixed at 1em 3em. auto looks silly when rendered
in a wide window.
Rescroll now at discretion of ish. Fixes issue with gist viewers not
scrolling.
URI now parses file:/// urls too. HTML files containing pigshell code
can be loaded using file:/// urls, don't necessarily need to be hosted.
jf -r can be used to read expressions from a file
join takes -s option to indicate that input streams are sorted. Tests
added.