Remove downloads plugin

This feature has been removed from the site and so the
plugin is no longer usable.

Closes #29
Document alternatives for oauth2 token more clearly

Closes #34
Reduce plugin dependencies

  * Removed maven-site-plugin
  * Made maven dependencies provided

Closes #33
Add initial Travis CI configuration
[maven-release-plugin] prepare release github-maven-core-0.6
[maven-release-plugin] prepare for next development iteration
Upgrade to github-maven-core 0.6
[maven-release-plugin] prepare release site-maven-plugin-0.8
[maven-release-plugin] prepare for next development iteration
Tweaked markup of settings