update README to include Docker container zzrot/alpine-caddy

updated README to include ZZROT's docker container that runs caddy on Alpine Linux inside of a Docker Container.

Fix for #721

Add Etag header

https: Faster tests

proxy: Allow mixed case Upgrade headers (WebSocket fix)

Caddy expects websocket to be completely lowercase.
Some applications send websocket upgrade headers like the following:
`Upgrade: WebSocket`

This change allows all variations of websocket.

tls: Customize key type with key_type

dist/init: caddy.conf for upstart

templates: Adding some useful utility functions

proxy: fix req.URL.Path for unix sockets

Correct unused assignments

golint is not part of the tests since our Markdown dependency defines
an interface that is not lint-compliant (unfortunately).
See https://github.com/russross/blackfriday/issues/240

Only bypass "bandwidth limit exceeded" errors on pushes

Add expvar middleware

Right now it has a very simple configuration:

	expvar /debug/vars

It will return a JSON object with memory statistics and the command line
used to start caddy, which are the two expvars that expvar registers by
default.

Add -restart=inproc option for in-process restart

cf. golang/go#12933

Middlewares can now make their own placeholders that may be useful in
logging, on a per-request basis. Proxy is the first one to do this.