Release 2.2.0

Merge branch 'master' into feature/update-jsx

2.x.x (dnsimple#125)

* Remove zone_delegates feature
* Enhance typespecs
* Rework structure of erldns_resolver module to reduce overuse of certain function names and separation of related functionality
* Apply standard formatting rules using rebar3_format plugin
* Start erldns_server_sup under the erldns_sup supervisor, fixes dnsimple#35 
* Add unit tests for resolver functions
* Use the RRFqdn instead of the zone name to look up RRSIGs in RRSet delete
* Always calculate the records_count and include it in the meta data for zone encoding

Feature/remove zone record lists (dnsimple#95)

Zones no longer hold their entire list of records as a field in the zone record. Instead there are two new tables in the zone cache: zone records, which is a list of records keyed on `{zone name, fully-qualified record name}`, and zone records typed, which is list of records keyed on `{zone name, fully-qualified record name, record type}`. Both ETS sand Mnesia storage backends are implemented.