ENH: Allow user to set the symbol lookup date
ENH: Allow user to set the symbol lookup date

Previously symbols were resolved to sids based on the end of
simulation date. This commit allows the user to specify the
date for which resolution will take place using a new
set_symbol_lookup_date() API method.

If the user does not use this method the lookup date will
default back to the simulation end date.

magne-max/zipline-ja,florentchandelier/zipline,CDSFinance/zipline,quantopian/zipline,MonoCloud/zipline,nborggren/zipline,Scapogo/zipline,umuzungu/zipline,DVegaCapital/zipline,nborggren/zipline,bartosh/zipline,grundgruen/zipline,quantopian/zipline,umuzungu/zipline,dmitriz/zipline,chrjxj/zipline,gwulfs/zipline,grundgruen/zipline,wilsonkichoi/zipline,humdings/zipline,CDSFinance/zipline,alphaBenj/zipline,MonoCloud/zipline,DVegaCapital/zipline,YuepengGuo/zipline,humdings/zipline,otmaneJai/Zipline,enigmampc/catalyst,michaeljohnbennett/zipline,dmitriz/zipline,Scapogo/zipline,gwulfs/zipline,otmaneJai/Zipline,bartosh/zipline,jimgoo/zipline-fork,sketchytechky/zipline,florentchandelier/zipline,YuepengGuo/zipline,alphaBenj/zipline,ChinaQuants/zipline,magne-max/zipline-ja,jimgoo/zipline-fork,wilsonkichoi/zipline,ChinaQuants/zipline,enigmampc/catalyst,chrjxj/zipline,sketchytechky/zipline,michaeljohnbennett/zipline