Added solr_group examples to README
Merge pull request #17 from jonasanso/solr_group-documentation

Added solr_group examples to README
fixed bug in solr_search parser, closes #12
fixed broken tests for mlt and stats
fixed missing params in man file for solr_group
added missing args group.format and group.func to solr_group
fixed sorting problem in solr_group, closes #13
sort param was missing within the solr_group fxn
also put in note in the docs to warn users that they need to return a field if they want to sort on it
added check for a url passed in to each fxn
removed group.facet and group.truncate from solr_group, closes #16
replaced data.table rbindlist fxn with rbind.fill #14 should be fixed,
fixed broken solr_mlt parsing, bumped version to v0.1.1
added test for solr_group, #19
added printed message of url called to every fxn, #20