Add support for unordered arrays

[kinbiko]

• Use the "<<UNORDERED>>" directive as the first string in the unordered array to ignore ordering when comparing arrays.
• Adds unit tests for this new logic.
• Adds a big real-world payload integration test that should cover most
  of the features of this package in combination

Closes #31

To do

There are still a few more changes that should be implemented before cutting a new minor release.

• Documentation in README
• Documentation in Go Docs
• Example test documentation
• Take this feature out for a spin on a real project.
• Self-review of the code