Thank you, Ross

Co-authored-by: Ross McFarland <rwmcfa1@gmail.com>

Addresses issues with changing between A, AAAA and CNAME records in
both directions with the Cloudflare API

See also: github/octodns#507
See also: github/octodns#586
See also: github/octodns#587

Increase Cloudflare page size to reduce request count

`GET zones` has a MAX of 50 and a default of 20
https://api.cloudflare.com/#zone-list-zones

`GET zones/:zone_identifier/dns_records` has a MAX of 100 and a default of 20
https://api.cloudflare.com/#dns-records-for-a-zone-list-dns-records

This dict is created earlier, presumably to speed up this exact lookup, but it was using the list form instead, requiring a linear scan for each item.

YAML configuration (see "CloudflareProvider" class docstring for details).

* spelling: ancillary
* spelling: antarctica
* spelling: australia
* spelling: authentication
* spelling: continental
* spelling: constructor
* spelling: conversion
* spelling: creation
* spelling: doesn't
* spelling: easily
* spelling: efficiently
* spelling: equivalent
* spelling: essentially
* spelling: everything
* spelling: exactly
* spelling: be
* spelling: expensive
* spelling: supports
* spelling: healthcheck
* spelling: immediately
* spelling: ignored
* spelling: invocation
* spelling: itself
* spelling: leftovers
* spelling: missing
* spelling: natural
* spelling: nonexistent
* spelling: peculiarities
* spelling: pointing

This change hit a line length limitation, so I'm wrapping it and
adding a period which appears to match local style...

* spelling: quicker
* spelling: response
* spelling: requested
* spelling: redirect
* spelling: traffic
* spelling: unknown
* spelling: uploaded
* spelling: useful
* spelling: separately
* spelling: zone

This will ensure that we have exactly the same logic/behavior across the
board when turning records into content and prevent the :-( hack that was in
here before. It was missing the max(min, ttl) bit we throw everything else
through and this makes that consistent. Most importantly it'll prevent us
from having to fix bugs or make improvements in multiple code paths in the
future.