Switch to JSON::MaybeXS

[schwern]

JSON.pm prefers JSON::XS which is maintained by Marc Lehmann who is someone I never want to expose a perl5i user to, he's horribly difficult to work with and JSON::XS hasn't had an update since 2013.

JSON::MaybeXS provides the same functionality as JSON.pm but uses the better maintained and more palatable Cpanel::JSON::XS (itself a fork of JSON::XS).

This also means we can recommend or even depend on Cpanel::JSON::XS for better performance without feeling guilty for feeding users to Marc Lehmann.