Futures:

    - Post and URL field parsing and editing.
    - Upstream proxies.
    - Strings view for binary responses.
    - Better manipulation of flows in mitmproxy: copying flows, adding
    comments.

Bugs:
    
    - In some circumstances, long URLs in list view are line-broken oddly.
    - When a bug in mitmproxy causes a stack trace, we hang on exit.