Snapshot

Add behavioral tests for examples from the YAML spec (#1835)

## Changes

I took the examples from https://yaml.org/spec/1.2.2.

The required modifications to the loader are:
* Correctly parse floating point infinities and NaN
* Correctly parse octal numbers per the YAML 1.2 spec
* Treat "null" keys in a map as valid

## Tests

Existing and new unit tests pass.