Version 0.4.3

• Add Haddock documentation to AST module. Many parts of the AST now have
  commentary on meaning and usage, and the Haddock page is sectioned.
• Add STATIC statement (should be similar/identical to SAVE attribute) to
  fixed-form lexer, support in Fortran 77 Extended parser.
• Rewrite post-parse transformation handling. Parser modules now export more
  parsers which allow you to select post-parse transformations to apply,
  intended to enable quicker parsing if you know you don't need to certain
  transformations.
• Support percent data references in fixed-form lexer, enable in Fortran 77
  parser
• Now also testing on GHC 9.0
• Cache INCLUDE-ed files to avoid unnecessary re-parsing