Update Rules, update schema file, add new test to validate XML

[mkavulich]

Description

This PR updates the standard name rules to fix some errors, resolve some omissions, and remove information that was moved elsewhere. It also updates the xsd schema file to properly account for the existing rules and XML format, and adds a test to validate the XML using the schema file.

Rules updates

• Add new bullets on the valid type elements, and validating the XML with the schema file
  • New valid types are integer, real, logical, character, complex, or ddt
• Remove "Generic Names" and "Chemical Species" sections that have been moved to the XML
• Make a note that you can use in_medium or of_medium as appropriate
• Fix several formatting issues

XML/schema updates

• Update schema to allow for nested sections; comments in standard names
• make type element optional and update for new rules as above
• Add a new test to validate the XML file using the schema file
• Fix a few malformatted XML entries

Issues

Resolves #136