Compression and minification of web resources

[btrask]

• We should build gzip versions of static files, and the static file server should prefer them if the request accepts gzip encoding
• We should consider compressing dynamic responses (which would also have the side effect of coalescing syscalls, which we currently don't do very well)
• We should minify our CSS and JS (although commonmark.js is by far the largest of these and it's already minified)