Pass command-line args to -main

[athos]

Currently, there is no way to pass command-line args to the -main function when -m is specified.
This PR provides the way to do that:

$ cat src/arith.clj
(ns arith)

(defn -main [op & args]
  (if-let [op' (case op "add" + "sub" - nil)]
    (let [args' (map read-string args)]
      (prn (apply op' args')))
    (throw (ex-info (str "Unknown op: " op) {}))))
$ trench -m arith add 1 2
3
$ trench -m arith sub 3 1
2
$

Also, -- can be used as a separator to distinguish arguments to pass to -main from the ones that should be passed directly to Trenchman:

$ trench -m arith -- add 1 2