#18 add --working-directory argument

[Paul E Johnson]

gnome-terminal has a handy CLI feature for launching a terminal, --working-directory. If you install that, then we can use MLterm as an "open terminal here" alternative in a file manager like Thunar or Nautilus.

[Araki Ken]

Thanks. I added --work-directory option.
https://bitbucket.org/arakiken/mlterm/commits/a2b07abf260bda25caf72465671418de6ca1c7cc