Consider changing handling of '<' and '>' characters in markdown documents

[jayhawk87]

Describe the bug

When trestle encounters the '<' or '>' characters, it considers these the start of an entity(?) tag and so consumes text until the next entity tag. As markdown linters use these characters to delineate bare HTML links, this can lead to strange error messages when comparing a document to it's template

To Reproduce

Steps to reproduce the behavior:

1. Establish a markdown template
2. Create a trestle document from the markdown template
3. Insert HTML links (i.e. https:...) into the document, delineated by '<' and '>' characters (for example, 'http://www.google.com')
4. Try to validate the document against the established template with trestle

Expected behavior

The document should pass the validation

Screenshots / Logs.

Example output as a result of this error:

Headings in the instance: /mnt/arch-design/ssad/privileged-access-gateway/privileged-access-gateway-ssad.md were removed. Expected 92 headings, but found only 88.
Heading #### Q.1.1 Personal IDs: in the instance: /mnt/arch-design/ssad/privileged-access-gateway/privileged-access-gateway-ssad.md was removed or not present
Heading #### Definitions: in the instance: /mnt/arch-design/ssad/privileged-access-gateway/privileged-access-gateway-ssad.md was removed or not present
Heading #### Definition: in the instance: /mnt/arch-design/ssad/privileged-access-gateway/privileged-access-gateway-ssad.md was removed or not present
INVALID: arch-design/ssad/privileged-access-gateway/privileged-access-gateway-ssad.md

If applicable, add screenshots to help explain your problem.

Environment

• OS: MacOS
• Python version: 3.11.11
• Installed packages: standard trestle install