return 0 (false), if s is not a member of the given string list. Otherwise return the item number (position of s in the list)
Examples:
#SHOW %ismember("abc","def|ghi jk|abc")
displays 3
#VAR friendsList {Zugg|Darker|Penny} #VAR petitioner zyxcef #IF %ismember(@petitioner,@friendsList) {cast heal @petitioner} {say Nope.}
sends 'say Nope.' to the mud.