Added windows_feature support for 2 new DISM attributes: all, source

Added a couple switches for the default DISM provider:
- 'all' will add the /all switch
- 'source' will add /LimitAccess /Source:"[source_string_provided]"

All is useful when components have dependencies and source is useful for loading on-demand stuff that you can pull locally if need be (like the NetFx3 package).
Also updated the README (including an example)