* Add initial dns.he.net provider support
* Update to new IncrementalDiff interface
* Fix ListZones output for `all` query on `get-zones`
* Refactor authentication code for 2FA with better error checking
* Fix integration test and refactor zone record retrieval
* Add option to use `.hedns-session` file to store sessions between runs
* Add comment on `session-file-path`
* Add integration test for TXT records longer than 255 characters
* Add additional checks for expected responses, and better 2FA error checking
* Minor documentation changes
* Revert "Add integration test for TXT records longer than 255 characters"
This reverts commit 657272db
* Add note on provider fragility due to parsing the web-interface
* Resolve go lint issues
* Clarify security warnings in documentation
