Provide parse functionality to aid in serialization

[ermik]

Description
This is a feature request.

Steps to reproduce the issue:

1. Use quad.ToString(quad.IRI("val")) to create "<val>"
2. Attempt to parse it using methods provided in quad package

Received results:
quad.MakeRaw which has been marked as deprecated, will produce correct results
quad.MakeIRI suggested in deprecation notice will create an IRI of IRI <<val>> which is invalid.

Expected results:
I expected to see a pair of methods clearly noted to be used from Marshalling and Unmarshaling quad.Value.