Excel 2003 Allows Html Entities

[oleibman]

Fix #2157. Excel 2003 format allows some things which a real Xml parser would reject. In particular, it permits Html entities, and leading whitespace. Change Xml Reader to do likewise.

This is:

• [x] a bugfix
• [ ] a new feature
• [ ] refactoring
• [ ] additional unit tests

Checklist:

• [x] Changes are covered by unit tests
  • [x] Changes are covered by existing unit tests
  • [x] New unit tests have been added
• [x] Code style is respected
• [x] Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• [ ] CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• [ ] Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate). If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.