NEW: Add migration guide between 0.3.x and 0.4.x.
NEW: Add migration guide between 0.3.x and 0.4.x.

lbdremy/solr-node-client,Bangsheng/solr-node-client,luketaverne/solr-node-client,nicolasembleton/solr-node-client,kfitzgerald/solr-node-client,yanxi-com/solr-node-client,lbdremy/solr-node-client,CondeNast/solr-node-client,godong9/solr-node-client