Implemented regex search in csvgrep.
Implemented regex search in csvgrep.

cypreess/csvkit,arowla/csvkit,aequitas/csvkit,dannguyen/csvkit,onyxfish/csvkit,tlevine/csvkit,haginara/csvkit,doganmeh/csvkit,nriyer/csvkit,snuggles08/csvkit,reubano/csvkit,themiurgo/csvkit,bradparks/csvkit__query_join_filter_CSV_cli,wjr1985/csvkit,gepuro/csvkit,elcritch/csvkit,metasoarous/csvkit,kyeoh/csvkit,KarrieK/csvkit,matterker/csvkit,jpalvarezf/csvkit,wireservice/csvkit,Tabea-K/csvkit,bmispelon/csvkit,archaeogeek/csvkit,unpingco/csvkit,barentsen/csvkit,moradology/csvkit,Jobava/csvkit