Rework _Route53Record to avoid a bunch of hacks

Quick-fix disable ALIAS for Route53 & Cloudflare

Cloudflare could potentially support it, but their details are different enough
that i'll need to be looked into specifically later.

Better to use something real/tested and less likely buggy/limited.

Skip planning (and populating) zones without elible targets

docs: Fix small typos

Alias support

Add support for ignored records.

Escape unescaped semicolons coming out of Route53

Fix zone-level always-dry-run functionality

Thanks @offmindby!

```yaml
ignored:
  octodns:
    ignored: true
  type: A
  value: 1.2.3.4
```

DnsimpleProvider updates delete before create, or else errors thrown

NS1 does not support SSHFP

Supports ALIAS for Dnsimple, Dyn, Ns1, and PowerDNS. Notes added to readme about
some of the quirks found while working with them. TTL seems to mostly be
accepted on ALIAS records so it has been added back, what it means seems to vary
across providers, thus notes.

Fix NS1 provider name

Update example class name from "octodns.provider.nsone.Ns1Provider" to working "octodns.provider.ns1.Ns1Provider".

Update README to include new NS1 Provider

First pass through NsOneProvider

They were working around the lack of class hierarchy, this addresses that by
adding 2 child classes. It gets rid of a bunch of ugly default params and
if-this junk in the main class that was trying to deal with plain & geo records.
Also as a positive side effect it gets rid of some hacks that lived in
Route53Provider dealing with the fact that the old setup couldn't detect going
to/from a GeoDNS record correctly.