2 websocket connections are made instead of one

Re-enable HTTP/2 for Go 1.7.

dist/init/linux-sysvinit: caddy for SysVinit

In addition to `linux-upstart` and `linux-systemd`, I think this one
might be very useful too.

The script is based on [this script](https://git.devuan.org/fredg/stuffs/blob/master/caddy/init.d/caddy)
by @fredg, found via [Installation du serveur Caddy sous Devuan · Frédéric Galusik](http://galusik.xyz/installation-caddy-server-devuan/#démon:d7570338f345f168f3c50f22e7f8c47c).
I have modified it into an extended version myself, since I had the need for this.

redir: loading block arguments before parsing matcher

fix issue #977
Signed-off-by: Tw <tw19881113@gmail.com>

 * Since Go 1.7 HTTP/2 support is enabled only if TLSConfig.NextProtos
   includes the string "h2".
 * see mholt/caddy#975

Specify the reload signal in the upstart script

Change position of locale directive

First, great job on the 0.9 release! It seems caddy's path lead into a bright future. Thanks also for including the locale plugin.

Trying it, I've figured out, that there might be a problem with the order of the directives. In the typical use case, the result of the locale detection might be used in the `rewrite` and `log` plugin. If I'm not mistaken, it makes sense to put the `locale` directive before those.

Register ratelimit

This reverts commit 9ea05919, reversing
changes made to 2125ae5f.

minor condition keyword check refactor

proxy: fix hyphen issue when parsing target

HTTP Headers

fix issue #948
Signed-off-by: Tw <tw19881113@gmail.com>

add a test to ensure this works.

* proxy: add benchmark
Signed-off-by: Tw <tw19881113@gmail.com>

* replacer: prepare lazily

update issue#939

benchmark            old ns/op     new ns/op     delta
BenchmarkProxy-4     83865         72544         -13.50%
Signed-off-by: Tw <tw19881113@gmail.com>

* proxy: use buffer pool to avoid temporary allocation
Signed-off-by: Tw <tw19881113@gmail.com>

Update readme contributing section

* 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