Support placeholder for args in option description

[lefou]

So, the following option taking one argument could be declared like this (from svn cmdline):

@CmdOption(names = { "--editor-cmd" }, args = { "PAR" }, description = "Use {0} as external editor")

and would give the folling line:

  --editor-cmd PAR   Use PAR as external editor

java.text.MessageFormat should be used. Translations should be supported, too.