Xml error logging

[adam-beauchamp]

Optimize xml schema validation performance

Previous brute-force validation logic had poor performance on non-validating xml documents.

Updated validation logic to:

• use simple string matching to guess the applicable schema for a document
• perform validation once

Added test cases for all schema version in

• test_valid_sixsicd.cpp
• test_valid_sixsidd.cpp

The jupyter notebook included in the request documents the verification strategy.