Add four new options and update README

  - Add support for SSSD. There are
    now two boolean values that support
    disabling and enabling SSSD and SSSD Auth.
    These are passed in as standalone flags.
  - Add support for PAM access via a boolean
    variable. This is passed in via 'extra flags'.
  - Add support for FORCELEGACY via a boolean variable.
    This is passed in via 'extra flags'
  - README includes descriptions of options
    functionality.
Fix typo in README
Change default for forcelegacy option

  - The default for forcelegacy is set to
    no, so the boolean of false is used to
    reflect that state.  Remove the previous
    default of undef.
  - Update the README to include the default
    in the example section.
  - Adjust order in which forcelegacy is displayed
    within the README example and within the parameters
    of the class.  Order change as a result of the
    configuration relationship between SSSD and forcelegacy.
Remove duplicate forcelegacy parameter.
Merge pull request #11 from Z3r0Sum/master

Additional Options/Functionality