This means that certificates don't accumulate in the conf directory, users
don't have to clear certificates if the CA is regenerated, and the user can
specify a custom CA without invalid certificates being loaded inadvertently.
- Move option parsing utiliities to proxy.py
- Don't have a global config object. Pass it as an argument to ProxyServer.
- Simplify certificate generation logic.
- Use templates for config files. We can re-introduce customization of the
certificate attributes when we need them.
- Split CA and cert generation into separate functions.
- Generation methods provide an error return when generation fails.
- When the user explicitly specifies a certificate, we don't generate it, but
fail if it doesn't exist.
