Extracting object from .load_instance_from_solr

Extracting .load_instance_from_solr to object

Extracting #active_fedora_class for SolrInstance

Tidying up SolrInstanceLoader#object

Adding spec for missing pid SolrInstanceLoader

Adding rudimentary doc SolrInstanceLoader

Extracting SolrInstanceLoader to separate class
Merge pull request #51 from jeremyf/feature-extract-solr-instance-loading

Extracting object from .load_instance_from_solr