Fix some load errors related to different gem versions being available

[phil-janeapp]

Context

The functionality introduced via #176 is great, but it has some subtle interactions with other libraries that are causing breaking bugs for us:

• Depending on the version of psych loaded, using YAML.load_file directly won't work if the config file contains aliases
• If MultiJson is present, JSON::Parser may not exist yet

Related tickets

• Add Schema validator #176

What's inside

• Ensure we utilize the wrapper for load_yaml to deal with aliases properly
• Utilize JSON::Validator.parse as it handles MultiJson and other inconsistencies

Checklist:

• I have added tests
  • Very difficult to add tests to this without moving to a multi-gemspec configuration. Not sure if that's worth it for this (although it might be)
• I have made corresponding changes to the documentation

[bibendi]

Hey Phil,
Sorry about that! Just one minor tweak, and I'll merge the changes.

[bibendi]

Thank you!

[bibendi]

@oleander FYI