allow message to be configured

Allow the message sent into the Campfire channel to be configured.
The permitted substitutions are in the config documentation. The
default message replicates the message currently displayed by
version 2.6 of the plugin.
Merge pull request #8 from tdyas/configure_message

allow message to be configured
[maven-release-plugin] prepare release campfire-2.7
[maven-release-plugin] prepare for next development iteration