add documentation on user configuration

It was very hard for me to figure out how to get the configuration from config.yml into the Session module, because I could neither find docs nor understand it from the code.
Dancer2::Session::Memcache => Dancer2::Session::Memcached
Reflect changes
Merge branch 'lbeesley-master'
erge remote-tracking branch 'upstream/master'

Conflicts:
	lib/Dancer2/Core/Role/SessionFactory.pm