4.0.0

#major: 4.0.0

Breaking changes for Serializers, Comparators & Reporters
- Now accept a Snapshot class as the argument
- Still have access to everything they had before via the getters
- Exposed lots more information for the serializer to customise the snapshot as desired

Snapshot Headers
- Users can now use custom headers via expect.header("A", "B").toMatchSnapshot(obj)
- These headers are serialized into the snapshot as a JSON Object
- Certain headers may be added as default in future versions

REGEX matching
- The Snapshot object is now parsed as a regular expression and key pieces of information are extracted

No more varargs
- Removed varargs param for `.toMatchSnapshot`.  It now only supports a single argument.

Remove onSaveSnapshotFile() hook
- This made the file difficult to parse via a REGEX