TODO: Mention OOM issues
Prevent some comments being run as doctests
manpage: Update for new demo page logic
Add a benchmark for ingestion
Restore per-item path-segment arenas
Make CRCs optional
Optimize PatchCache::push_line()
Remove a redundant clone

This actually makes a huge difference to ingestion performance.
explorer: Get GTK demo working again
Limit the total number of open FDs
Support restarting an ItemBuilder

Also, move more logic into PatchCache.
Share path segments globally; separate Item and PatchCache
TODO: Add the "too many open files" bug
demo: Use more horizontal space
Don't use accepted MIME types to change behaviour

Special-case "index.html' instead.
demo: Use innerText rather than innerHTML
Update the TODO list
Fix a broken unit test
Handle bad Accept-Encoding headers gracefully
Generalise the header parser to encodings