Add support for include_archived & exclude_projects to the exporter

[syphernl]

I've made a few improvements to the export script:

• Added support for excluding archived projects (include_archived=False). Defaults to False.
• Added support for excluding (partial/regex based) projects (exclude_projects). This is useful if there are projects you do not want to export (e.g. if they are too big)
• Added a no-op mode to only show which projects would be exported but not actually run the export. (use -n or --noop flag)
• Tweaked the Readme

[rvojcik]

Hi @syphernl ,

nice work man !
Thank you much for your contribution