afvs[?] manipulate sp based arguments/locals

• afvs list stack based arguments and locals
• afvs* same as afvs but in r2 commands
• afvs [idx] [name] [type] define stack based arguments,locals
• afvsj return list of stack based arguments and locals in JSON format
• afvs- [name] delete stack based argument or locals with the given name
• afvsg [idx] [addr] define var get reference
• afvss [idx] [addr] define var set reference