Only inline forwarding is supported for now.

References: https://todo.sr.ht/~sircmpwn/koushin/37

Latest linkify contains a fix for e-mail addresses surrounded by angle
brackets.

Loading remote resources by default has privacy implications.

This reverts commit 02faf6174b.

This commit doesn't work, because it's applied to <img> tags. Making it
handle <a> tags doesn't work either because bluemonday will strip any
target="_blank" attributes, making the compose form open in the
<iframe>. Let's just revert this whole commit for now.

Closes: https://todo.sr.ht/~sircmpwn/koushin/33

Closes: https://todo.sr.ht/~sircmpwn/koushin/64

Fixes: 9d76488235 ("readme: add hint about SourceHut theme")

This makes it easier for people to try out koushin.

Don't issue a CardDAV query with any filter, Google won't return any
result.