Topographica versioning with param.Version

This is the corresponding pull request to the [one in param](https://github.com/ioam/param/pull/57). It uses param.Version to set the same variables as before (topo.release, topo.commit, topo.version) and set topo.\_\_version\_\_.

Of course this will have to be merged after the one in param and will have to include the appropriate submodule reference update.