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.

Reflow all bash scripts

fastcgi: Add `except` to FastCGI. Minor refactor in proxy.

    When thy variables henceforth accept blessed white-space,
    guided will thy scripture be along righteous path(s).

    -- 4 BASH 3:42

Caddy's dist files sometimes ended up being owned by matt:staff or other
quite arcane and/or frightening names. If someone extracting didn't pay
attention a regular user who happened to have same uid by accident could
later tamper with the files' contents. It's 0:0 from now on.

Use all available threads when packaging distributables
Caddy binaries will be added to their archives in-place: This change
eliminates them being renamed within dist/builds one after another.
As does 'gox', dist/automate.sh will spare one available thread if possible.

Format of main.buildDate has been locale-dependent,
and is now ISO-8601 compliant.

Caddy displayed with ```-version``` something like (mind the datetime format):

    Caddy 0.8.2 (+591b2090 Fri Mar 18 21:22:55 UTC 2016)
     2 files changed, 9 insertions(+), 4 deletions(-)
    build.bash
    main.go

which is now:

    Caddy 0.8.2 (+591b2090 2016-03-18 21:22:55Z)
     2 files changed, 9 insertions(+), 4 deletions(-)
    build.bash,main.go

See also:

 * http://wiki.bash-hackers.org/scripting/obsolete
 * https://google.github.io/styleguide/shell.xml
 * https://xkcd.com/1179/

Support for case insensitive paths using CASE_SENSITIVE_PATH env var.

pprof: Adding pprof middleware for profiling caddy.

Update unit files for systemd

Unlike network.target the network-online.target guarantees that the network
devices are online.

If you bind to 0.0.0.0, [::], [::1], and/or 127.0.0.1 only that is enough to
proceed. But in case a particular IP is needed, like ${COREOS_PUBLIC_IPV4},
we require any IP assignments to have completed before Caddy's start. That
is achieved by depending on systemd-networkd-wait-online.service (which is
scheduled before network-online.target, then, automatically).

Fix for #659.

systemd unit file

Add systemd service file for caddy

Add some README with basic setup instructions

Explain how to view the service configuration

Add a note about permissions

Add a comment about run user and group

service->service unit

A systemd service can consist of different units. A unit configuration
file has the `.service` file ending which is a bit confusing, so please
be considerate if I'm confusing `service` and `unit` in the README

Fix typos/reword

Add contact information

markdown: Included files in Markdown templates have access to document vars

Refactor how middleware.Context includes files

mime: Use a map, and error on duplicate extensions.

 - The mime middleware used filepath where it should arguably use path.
 - Changed the configuration to use a map instead of scanning an array
   during every request.  The map is static (after configuration), so
   should be fine for concurrent access.
 - Catch duplicate extensions within a configuration and error out.
 - Add tests for new error case.

proxy: Add max_conns parameter for per-host maximum connections

Play nice when ACME used manually.

Add flag to list directives.

Folder for init scripts within dist / FreeBSD service script