Add Route53 zone functions

[rawiriblundell]

Hi Mike,
I've added a couple of Route53-specific functions that enhance r53 interactivity in the following ways:

I suggest the introduction of the r53- namespace. This makes it clear to the end-user that Route53 is the service is being used. This aligns with other examples like rds-* and lambda-* and encourages a move towards consistent namespacing.

It might be the case that lib/domain-functions adopts this approach as well e.g. domains() -> r53-domains()

I've left the existing hosted- and domain- functions alone to keep this from being a breaking change. In theory the code for hosted-zones and hosted-zone-ns-records can be removed, with aliases implemented in a way to maintain backwards compatibility. For example, something like this:

alias hosted-zone-ns-records='${BMA_HOME:-$HOME/.bash-my-aws}/bin/bma hosted-zone-ns-records'

Could instead be:

alias hosted-zone-ns-records='${BMA_HOME:-$HOME/.bash-my-aws}/bin/bma r53-zone-records --type NS'

The command reference update also lays out a few other enhancements that I've added.

This hypothetically also supersedes #252