Module cleanup, docs cleanup, bug fixes

• Provide a couple of real-life examples in docs
• Convert plugin order list into table
• Update welcome page and module documentation
• Handle invalid dates, paths and urls
• Consider ticket description change as update
• Check free command line arguments for typos
• Include example config in docs, adjust man page
• Fix the --debug option, prevent logger duplication
• Correctly handle missing config file
• Move Options.time_period() to Date.period()
• Update source url, add python-bugzilla to requires
• Move stats classes into a separate module
• Completely remove get_color_mode/set_color_mode
• Adjust utils.pluralize() to take a single argument
• Adjust commit-msg hook to handle comments
• Move command line code to the did.cli module