Merge branch 'v2.1.x' into v2.2.x

* v2.1.x:
  (maint) Add semantic versioning info to README
  Docs: Clarify the use case for the anchor type
  Docs: Remove author emails from stdlib functions
  Docs: Copyedit function doc strings
  Docs: Correct indentation of markdown code examples
  Docs: Update documentation of stdlib classes
  Docs: Update file_line documentation
  Docs: Improve example in merge function