Fix phpDoc return type
Add support for HTTP DELETE requests
Add support for adding/deleting/getting synonyms for the Solr client
Update Solr synonyms when editing search queries in AdminHtml
Add ToDo comments
Merge remote-tracking branch 'origin/synonyms'

* origin/synonyms:
  Add ToDo comments
  Update Solr synonyms when editing search queries in AdminHtml
  Add support for adding/deleting/getting synonyms for the Solr client
  Add support for HTTP DELETE requests
  Fix phpDoc return type