(PE-5503) Support for configuring a server certificate chain

This commit adds support for configuring a server certificate chain
(including the end certificate and any CA certificates) which the
server can deliver to the client for the client's use in validating the
server.

Previously, only a single server certificate could be configured,
without the full chain of trust.  The commit adds support for a new
optional `ssl-cert-chain` setting which can be used to configure the
set of CA certificates to append to the certificate from the `ssl-cert`
setting.
(PE-5503) Added -pem to end of function names to clarify intent

This commit changes the name of the `get-x509s-from-ssl-cert` function
to `get-x509s-from-ssl-cert-pem` and the name of the
`get-x509s-from-ssl-cert-chain` function to
`get-x509s-from-ssl-cert-chain-pem` in order to make the intention of
the supplied arguments to each a little more obvious.
(PE-5503) Clarify certificate order intent for `ssl-cert-*` settings

This commit alters the description of the `ssl-cert` and
`ssl-cert-chain` settings in an attempt to better clarify the order in
which certificates should appear in PEM files.
Merge pull request #67 from camlow325/feature/master/PE-5503-present-server-cert-chain-for-ssl

(PE-5503) Support for configuring a server certificate chain