Improve logging

[bitprophet]

Right now logging is scattershot and uses ye olde local sys.stderr.write functionality, with bonus "rebind to a partial within functions due to requirement of access to app.config to tell whether debug mode is enabled" BS. (The latter being partly Sphinx/docutils' fault, but still.)

Would be nice to:

• Figure out a non awful way to access the config value globally
  • Given that this is a documentation building tool (i.e. not expecting long, persistent processes where state might get confused) & there's difficulties in obtaining the data from Sphinx at arbitrary points in time...I might stoop to "set a module level variable at some point".
• Replace hand-rolled log function with actual logging module (stdlib or other)
• Overhaul actual log lines to be clean, useful, thorough etc.
  • Because it's really dumb to add manual log/print statements when debugging new features or bugs. It's 2016.