Fix a problem with NSTask blocking the main thread.

NSTask seems to block the app while the shell command is running.
Added an option to `shell` to run in background and ignore the output.
More options can be added to `options` parameter as needed.

Example:

bind "S", ["cmd", "alt", "ctrl"], -> shell '/usr/bin/say', [api.selectedText()], null, null, {"donotwait": true}
Modified `shell` API method.

Removed "pwd" and "input" parameters and added them to "options".
Added `minimize` and `unMinimize` to Window class.

This allows to focus a window when it's minimized.

Example:

bind "M", mash, ->
  for w in api.allWindows()
    if w.title().indexOf("mutt") != -1
      alert w.title()
      if w.isWindowMinimized()
        w.unMinimize()
      else
        w.focusWindow()
Added `show` and `hide` to App.
Merge pull request #8 from djromero/master

Fixes a problem with NSTask blocking the main thread.