Generate the zone name following the spec of Google Cloud DNS

Zone name must begin with a letter, end with a letter or digit, and only contain lowercase letters, digits or dashes, and be 63 characters or less.
For instance, a reverse zone of IPv6 may violate the spec on the first character and the length of the zone name.

Support for SSHFP ECDSA (3) and SHA-256 (2)

Fix SRV and SSHFP record for OVH provider

RFC 6594 & RFC 7479

Option to handle Cloudflare proxied records

Add SRV support to Cloudflare provider

This change imports records that are marked as proxied so that they can be synced to other DNS providers as described in
[this support acticle](https://support.cloudflare.com/hc/en-us/articles/115000830351-How-to-configure-DNS-for-CNAME-partial-setup-when-managing-DNS-externally).
Records that use this functionality will be ignored by this provider and not be synced back to Cloudflare as we don't know the origin record values that would be required.

This change does not allow you to enable, disable or configure the CDN itself as that would require a lot of metadata to be handled by OctoDNS.
The intention of this change is to allow users to run a multi-DNS provider setup without sending any traffic to their origin directly.

See also github/octodns#45

Dnsmadeeasy provider

Handle MX preference of 0

RateLimitException.period is coming back as str now

Comment that NS1 geo health checks aren't yet supported

Set Ns1Provider to "Yes" for GeoDNS Support