Moves AppArgumentParser into options module.
Moves Recorder concern out of Engine.
Refactor some Engine methods.
Implements --retry-connrefused, --retry-dns-error.
Sets default for --tries to 20
Refactor WARCRecorder to save files in --warc-tempfile.
Removes saving both http and content files.

Saving the http file is sort of redundant and may use up valuable disk
space.