Fix: '.md' to '.html' with anchors (fixes #1415)

Markdown documentation can now reference another markdown file with an anchor and it will work for the site along with github.
ex. `working-with-rules.md#rule-unit-tests`
0.9.2
Revert "Fix: '.md' to '.html' with anchors (fixes #1415)"
New: Add operator-assignment rule (fixes #1420)
Fix: Adds clamping to getSource beforeCount (fixes #1427)

- Without the clamping in place, there is the possibility of passing
  negative values to string.slice and winding up with odd results.