don't use // in xpath while parsing xml in solr_request
wrote specs for merge service merge method - one still failing
add comment explaining Item doc attribute
added comments about SolrDocument model attributes
refactored solr_request process_add for readability
revise comment for merge_service.merge_item_hashes
add more comments to merge_service
fix failing merge_service.merge spec
SolrRequest:  make delete_ids a private method;  process_delete should process all ids in a single request
start specs for solr_request delete functionality
add more delete tests and don't send solr add if SolrDocument from merge service is empty
finish solr_request delete specs