This commit fixes issue #89 where anchor validation fails on links like
`../file.md#anchors` when the anchor is defined using HTML `<a name="...">`
tags instead of `<a id="...">` tags.

Changes:
- Updated HTML_LINK_PATTERN to match both 'id' and 'name' attributes
- Changed from greedy to non-greedy matching to handle multiple anchors
  on the same line
- Modified contains_anchor() to use re.findall() instead of re.match()
  to find all anchors on a line
- Added comprehensive test cases for HTML anchors with both id and name
  attributes, including anchors in table cells and with dots in names

The fix is backward compatible and handles:
- Legacy <a name="..."> tags (commonly used in tables)
- Modern <a id="..."> tags
- Multiple anchors on a single line (e.g., in table rows)
- Anchors with special characters like dots (e.g., REGISTER.FIELD1)

Fixes #89

Co-Authored-By: Claude <claude@anthropic.com>