Improve Testing (remove /tmp and use unittest & hypothesis)

[Teque5]

Somewhat as a reminder to myself, several tests including those in test_sigmffile can be generally improved:

• Ensure all tests use unittest framework.
• Remove references to /tmp and use tempfile instead. (remove explicit use of /tmp & address pylint issues #105)
• Ensure all tempfiles cleaned up (some still created by test_archive).
• Use hypothesis where possible.