Add support for fields parameter in get operation
Add support for fields parameter in get operation

Update the getDocument method to return the `fields` field instead of `_source` if available.
Allows to get a document from ES and specify the fields you want (See fields section at http://www.elasticsearch.org/guide/reference/api/get/)
Gasol/Elastica,falconavs/Elastica,im-denisenko/Elastica,pborreli/Elastica,vend/Elastica,webdevsHub/Elastica,idio/elastica,piotrantosik/Elastica,eilgin/Elastica,JustinHook/Elastica,Southparkfan/Elastica,Southparkfan/Elastica,giovannialbero1992/Elastica,falconavs/Elastica,p365labs/Elastica,Tobion/Elastica,miniplay/Elastica,pborreli/Elastica,kartikm/Elastica,tmatei/Elastica,webdevsHub/Elastica,JustinHook/Elastica,vend/Elastica,splitice/Elastica,markeilander/Elastica,sugarcrm/Elastica,ebernhardson/Elastica,kartikm/Elastica,sugarcrm/Elastica,ruflin/Elastica,jeancsil/Elastica,p365labs/Elastica,im-denisenko/Elastica,giovannialbero1992/Elastica,markeilander/Elastica,jeancsil/Elastica,stof/Elastica,Mosoc/Elastica,ewgRa/Elastica,Mosoc/Elastica,ARAMISAUTO/Elastica,revinate/Elastica,eilgin/Elastica,Jmoati/Elastica,ARAMISAUTO/Elastica,vlajos/Elastica,stof/Elastica,giorrrgio/Elastica,0x46616c6b/Elastica,tmatei/Elastica,giorrrgio/Elastica,vlajos/Elastica,vend/Elastica,idio/elastica,Tobion/Elastica,0x46616c6b/Elastica,piotrantosik/Elastica,fubuki/Elastica,miniplay/Elastica,ewgRa/Elastica,Gasol/Elastica,revinate/Elastica,Jmoati/Elastica,fubuki/Elastica,ebernhardson/Elastica