* Allow for UDP servers

Extend the Server interface with ServePacket and ListenPacket - this is
in the same vein as the net package.

Plumb the packetconn through the start and restart phases.

Rename RestartPair to RestartTriple as it now also contains a Packet.
Not that these can now be nil, so we need to check for that when
restarting.

* Update the documentation

fix: import should always be relative to current file directory

fix transparent host header #916

* import should get absolute path before glob

* fix test: import should get absolute path before glob

* try to fix test on windows

* use complete path as the dispenser filename

* fix caddyfile test

* Prototype middleware Config

* Refactors

* Minor refactors

discard remaining args for if block in redir.

fix rewrite if problem (skip remaining args)

* Initial concept for pluggable storage (sans tests and docs)

* Add TLS storage docs, test harness, and minor clean up from code review

* Fix issue with caddymain's temporary moveStorage

* Formatting improvement on struct array literal by removing struct name

* Pluggable storage changes:

* Change storage interface to persist all site or user data in one call
* Add lock/unlock calls for renewal and cert obtaining

* Key fields on composite literals

Changing refs from /usr/bin to /usr/local/bin

Thanks to @jaredfolkins for the feedback

Test that the host header forwarding on proxy

Support for placeholders in fastcgi env vars.

This is inconsistent with the other directives, but import is a special
case and frankly the behavior of import shouldn't change depending
on the directory from which you run caddy. Breaking change but I think
it's for the better, and best to do it now before 1.0.

Also see
https://forum.caddyserver.com/t/caddy-0-9-beta-version-available-updated-beta-2/146/29?u=matt
which has another account of strange proxy behavior; I think this
resolves that.

Also a few little formatting changes and comments.

If we listen on 127.0.0.1:80 for `localhost` but :80 for everything else,
then a hostname in the hosts file that resolves to 127.0.0.1 will be
served on :80 (unless the bind directive is used) but the OS will use
the socket listening at 127.0.0.1:80, thus giving a "No such site" error
even though the site is there, but it's on the other listener at :80.

Two ways to fix this: 1) Leave as-is and require the user to set "bind
127.0.0.1" in their Caddyfile for all sites that are resolved in the
hosts file, or 2) Take out this special case and let localhost sites
listen on :80 (unless the user changes that with the bind directive, of
course). Having localhost bind to any interface is a little annoying
(unsettling?) but probably best in the long run.

https://forum.caddyserver.com/t/wildcard-virtual-domains-with-wildcard-roots/221/9?u=matt

Add filemanager directive