SPF relaying and MAIL FROM 

* SPF: skip HELO tests for IP literals

* SPF: added [relay]context setting. When a connection has relaying permission and context=myself, use  Haraka's public IP in the SPF mfrom query to determine if Haraka has permission to send on behalf of that MAIL FROM domain.

* Added options for setting defer/deny settings for helo/mfrom when connection.relaying=true.

* spf.ini emptied. Any settings in existing spf.ini files are honored. Settings are all documented in spf.md.