This causes the mailbox to automatically reload the page every 60
seconds, without JavaScript.

This also updates the base template data to include the full URL, and
replaces the earlier "Path" field with a pre-split array of path
components, which is more immediately useful to most templates given the
limitations of string munging with text/template primitives.

There's no way around having a global mutex, because we need to update
the HTTP routes when reloading plugins. During reload we need to lock
the whole server.

Closes: https://todo.sr.ht/~sircmpwn/koushin/43

This only reloads templates for now. In the future it'll also reload
Lua plugins.

This allows to access the request metadata and the session from injectors.

This allows Go plugins to easily inject global data.

RenderData will be used for an interface.

Now that all templates are provided by plugins, there's no need to have
a public/ directory. Themes can be in /themes instead of /public/themes.

This plugin offers base IMAP/SMTP functionality.

References: https://todo.sr.ht/~sircmpwn/koushin/39

And unexport a few internal functions.

This allows plugins to access it.

GlobalRenderData contains some global metadata that can be obtained from
any template.

RenderData is a base type for template data. It contains a Global field
with global metadata and an Extra field for plugins.

This is the first step to allow each user to have a different theme.

This function doesn't render anything, it just adds extra data to the
template data.

References: https://todo.sr.ht/~sircmpwn/koushin/1

Closes: https://todo.sr.ht/~sircmpwn/koushin/14