Merge tag '0.2.1' into develop

Tagged version 0.2.1
Removed 'Solr' prefix from class names
Separated Connection class into Core and Client
Added ->ping()
Fixed invalid exception
Added Client::coreStatus()
Added Client::getEmitter()
Replaced InstanceTrait with Solr factory class.
Improved tests
fixed missing backslash in namespace
Added license info to composer.json
Updated changelog for 0.3.0 release
Merge branch 'release/0.3.0'