Parsing: Auto set by() option

[gvegayon]

-parallel- should automatically recognize when a command contains the -by- prefix. This can also apply to commands such as -collapse-, -reshape- and -compress-.

if ("`by'" == "") {
    if (regexm(`"`cmd'"',"^by ([a-zA-Z0-9_ ]+)") {
        local by = regexs(1)
    }
}