Remove old commented out code for keyring generation in GPG.__init__().
Update docstring for GPG.genkey().
Add docstring for GPG.gen_key_input().
Add key generation utility functions.

 * Add util._make_passphrase() for creating a random string passphrase and
   optionally writing it to a file only readable by the real uid of the
   running process.
 * Change the util._today() function to _next_year(), which gives us today's
   date a year from now, for setting the default expire date in
   GPG.gen_key_input().
Remove unused code from the unittest runner.
Only create one test directory while running unittests.
We don't have a default Name-Comment in gen_key anymore, so change unittest.
Add listkeys tests to Makefile command.
Fix the super() calls in ResultStringIO in unittest script.
Add unittest for _copy_data().
Fix missing method calls in unittest for GPG.list_keys().
Move _copy_data(), _write_passphrase(), and _threaded_copy_data() to util.
Make the util module private.
Get rid of the "--no-show-photos is deprecated" GnuPG warning.
Merge branch 'feature/cleanup-api' into develop