kibana: Add a Kibana image

Dump a Kibana tarball into Nginx's htdocs, and use an
ELASTICSEARCH_URL environment variable to adjust config.js at spin-up.

List Kibana after Nginx in build.sh's REPOS to ensure the Nginx image
is built first.
memcached: Add a Memcached image

The 10MB of overhead memory were estimated from this output in a
running memcached container:

  # ps aux
  USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
  root         1  0.0  0.0  20300  2124 ?        S    20:57   0:00 /bin/bash
  memcach+   184  0.0  0.0 323124  1112 ?        Ssl  20:58   0:00 /usr/bin/memcached -d -p 11211 -U 11211 -m 128 -c 1024 -u
  root       224  0.0  0.0  25064   440 ?        S    20:58   0:00 supervising syslog-ng
  root       225  0.3  0.0 124708  3620 ?        Ssl  20:58   0:00 /usr/sbin/syslog-ng --persist-file /var/lib/syslog-ng/sysl
  root       263  0.0  0.0  18632   804 ?        Ss   20:58   0:00 /usr/sbin/cron
  root       300  0.0  0.0  15440  1148 ?        R+   20:58   0:00 ps aux

Less Bash and ps, that's 1112 + 3620 + 804 = 5.5MB of resident memory,
so 10MB seemed like a safe buffer.
Use envsubst instead of sed to parse Dockerfile.template

Convert everything in one pass, instead of taking a separate pass for
each variable.  Thanks to aluedeke for mentioning envsubst on #docker;
I hadn't heard of it before.  It's distributed as part of gettext [1],
and not in POSIX [2], so it may be slightly less portable.  However,
envsubst and gettext are in Gentoo's x86 and amd64 stage1s, so it
can't be *that* uncommon ;).

[1]: http://www.gnu.org/software/gettext/
[2]: http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html
build.sh: Bump DATE to 20131226 to match the new weekly build
redis/Dockerfile.template: Direct logs to syslog

Since I'm tailing /var/log/messages in CMD.  This also makes it easier
if you want to redirect the logs to a central syslog server.
portage/README.md: You can mount volumes from stopped containers

As Sven Dowideit describes in a pending doc update [1].

[1]: https://github.com/dotcloud/docker/pull/3389
postgresql: Declare /var/lib/postgresql a VOLUME

Avoid the hassle of maintaining a host-mounted volume by letting
Docker handle the volume maintenance ;).  We need to declare the
VOLUME *after* filling it with content (with 'emerge --config'),
otherwise ownership and permissions on the empty volume are lost
[1,2,3], and future RUN commands die due to:

  initdb: could not access directory "/var/lib/postgresql/9.3/data": Permission denied

[1]: https://github.com/dotcloud/docker/issues/2360
[2]: https://github.com/dotcloud/docker/issues/2969
[3]: https://github.com/dotcloud/docker/issues/2975
[4]: https://github.com/dotcloud/docker/pull/3008
nginx/Dockerfile.template: Change default hostname to _

From the docs [1]:

  In catch-all server examples the strange name “_” can be seen:

    server {
        listen       80  default_server;
        server_name  _;
        return       444;
    }

  There is nothing special about this name, it is just one of a myriad
  of invalid domain names which never intersect with any real name.

Still, an invalid domain name makes more sense than 'localhost' for a
public server.

[1]: http://nginx.org/en/docs/http/server_names.html#miscellaneous_names
nginx-proxy: Add an Nginx proxy image

I've got a bunch of HTTP server images, but I need a single proxy
container that supports SNI to expose them to the world.  This
container can link to a colleciton of HTTP-serving containers and
proxy them under arbitrary hostnames using user-supplied, per-host
certificates and keys.

env and sed are both in POSIX 2013 [1,2], and the:

  eval A=\$$B

variable indirection is because POSIX [3] doesn't support Bash's
indirect expansion "A=${!B}".  The 'tcp' -> 'https' replacement maps
Docker's tcp:://${IP}:${PORT} addresses to https://${IP}:${PORT} for
use in the Nginx config.

envsubst is in gettext [4] and not in POSIX [5], so it may be slightly
less portable.  However, envsubst and gettext are in Gentoo's x86 and
amd64 stage1s, our Gentoo-based images will have it.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/env.html
[2]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sed.html
[3]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02
[4]: http://www.gnu.org/software/gettext/
[5]: http://pubs.opengroup.org/onlinepubs/9699919799/idx/utilities.html