Clean up project.clj.

Relates to #113.

- remove undocumented :namespaces
- simple alias doesn't require vector
- order changed to the one used in the official documentation
- add url and license metadata
- build aborts on conflicting dependency versions
- uberjar profile fixes warning that main will be no longer included in
  aot by default with lein 3.x
Remove lein-ring plugin.

Fixes #113.

Because we provide our own main method the plugin is not longer used.
Merge pull request #115 from mvitz/remove-lein-ring-plugin

Remove lein ring plugin.