Merge lp://staging/~rcj/vmbuilder/mfdiff_fixups into lp://staging/~ubuntu-on-ec2/vmbuilder/mfdiff

Modernization and fixes

Break up main(), modernize code, improve documentation and variable
naming, python3 compat, misc fixes, urllib to requests migration,
support non-x86 architectures, and add logging.

This requires python-six version newer than what is shipping in some
supported Ubuntu releases to use six.viewkeys. (>=1.10 is preferable)

 [ Robert C Jennings ]
 * Strip architecture from binary when searching cache
 * Copy rather than rename changelog files
 * Force output to UTF-8 at all times
 * Output utf-8 rather than ascii
 * Change exception rendering for python3 compatibility
 * Use the current directory for temp changelog files
 * Improve variable naming for changelog_url (was clog_url)
 * Support non-x86 architectures
 * Fix usage text to correct option order
 * Eliminate traceback if binary package has been renamed
   (no longer in apt cache)
 * Use a real temporary file
 * Fixups for code-review
 * Improve names in print_changelogs and store more to the sources dict
 * Break out changelog processing from main
 * More variable renames
 * Rearrange summary printout and changelog printing for later refactor
 * Name, spelling, and doc cleanup
 * Stop processing source package on exception
 * Unlink temp file only if it exists
 * Add more complete function docstrings
 * Additional refactoring to reduce size of main
 * isort requests
 * Update authors/copyright
 * Add logging
 * Simplify cmdline --verbose option
 * Swap urllib for requests
 * Improve variable naming
 * Consistent sorted output
 * python3 compatibility changes
 * Document functions, use 'with' for files, and minor fixes
 * [merge] PEP8 cleanup, example updates, & python-apt updates
   * Correct vi line for tab expansion
   * README: Remove trailing spaces
   * Use host apt-secure keychains
   * APT version comparison moved from apt to apt_pkg
   * Remove unused cmdline option
   * Update README to use modern examples
   * Move comment to proper function
   * remove unused imports/variables
   * sort imports
   * pep8: autopep8 changes
   * pep8: tab -> space conversion