API Add support for Solr 4 and make it the default

Solr::configure_server now takes "version" as one of the keys in the
option array, and behaves slightly differently depending on whether
that version is 3 or 4, to provide support for both Solr versions.

The Solr extras and templates have also moved, so that different
versions can be provided for the two different Solr versions.
Merge pull request #35 from hafriedlander/solr4

API Add support for Solr 4 and make it the default