Improve dice command and its help

This adds spaces between the generated numbers for multiple dice (previously gave results in the form 10,23,14 etc; this causes it to be 10, 23, 14 etc). It also prints the sum of all random generated numbers if more than one is generated at once, and documents the syntax for rolling multiple dice in the help for dice. 
Unrelated to dice but in this pull request is adding /dexsearch to the list of informational commands given by /commands or /help.