name of the application (to show in the help message)
short description of what the application does (should be one line only, preferably less than 80 characters long)
how the application is supposed to be invoked
long description of what the application does and how to use it
string to use as the short prefix (defaults to '-')
string to use as the long prefix (defaults to '--')
character to use as the explicit assignment symbol (defaults to '=')
Constructor.