This is a first pass, and any comments would be appreciated.

This is mostly a code reorganization to simplify building the
docker image.

It allows the initial groups/clusters to be set via environment variables
using the following format:

export MEMCACHED_GROUPS=2
export MEMCACHED_GROUP_0_NAME=docker
export MEMCACHED_GROUP_0_HOST_COUNT=1
export MEMCACHED_GROUP_0_HOST_0=memcached
export MEMCACHED_GROUP_0_PORT_0=11211
export MEMCACHED_GROUP_1_NAME=cluster
export MEMCACHED_GROUP_1_HOST_COUNT=2
export MEMCACHED_GROUP_1_HOST_0=memcached01.example.com
export MEMCACHED_GROUP_1_PORT_0=11211
export MEMCACHED_GROUP_1_HOST_1=memcached02.example.com
export MEMCACHED_GROUP_1_PORT_1=11211

The docker-compose.yml file is another example of how to optionally
pass in default values.

It also has a small fix for xss checking in src/Library/Bootstrap.php
that recursively checks values that are passed in as an array instead
of skipping them.

This is a first pass to make it easy for developers to get this up
and running on their local machines without needing to know too
much about how to set up a php application, and easy for there to be
a set of default configs that "just work" without needing to burn a new
docker image.