Add support for demo mode in docker.

roundup/demo.py
  Make changes to allow exposed port in docker to be specified
  separately from the port that demo mode binds to. Also permit
  bind address specification as well.

roundup/scripts/roundup_demo.py:
  Update required by changes in demo.py.  Also move away from
  positional arguments to prefer flag arguments. Required for
  passing port and host specification. Flake8 fixes.

share/man/man1/roundup-demo.1
  Document use of option flags rather than positional
  params. Other cleanups.

doc/installation.txt:
  Document new docker modes: demo, shell and admin.
  Update docs:

   overview section - reorg, added template info

   for the impatient section - added docker demo mode reference,
            more docs on top level demo.py use.

   new section on docker demo mode

   removed getting roundup section. folded into installing roundup.
       also prior for the impatient section describes how to download.

   install via pip in venv recommended supported method

   document all provided templates. not just minimal and classic.

   added index references.

   move sections around, decreased sectin depth, reformatting

scripts/Docker/roundup_healthcheck:
  When running roundup-demo, there is no tracker spec. So default to
  demo if no tracker=directory args found. Prevent's docker from
  reporting an unhealthy container when running demo.

scripts/Docker/roundup_start:
  implement demo, shell, admin docker modes.

Author: rouilj

CHANGES.txt

@@ -92,6 +92,10 @@ Fixed:
   directory. This better identifies the directory when copied into
   the Zope framework. It also matches existing
   documentation. (John Rouilard)
+- Dockerfile supports demo mode for instant gratification
+  8-). Also supports shell and admin mode (John Rouillard)
+- Multiple fixes/updates for installation documentation.
+  Including docker shell/admin/demo mdoes. (John Rouillard)
 
 Features: