Version 0.6.0

• IF and CASE block constructs are now parsed as blocks at parsing instead of
  as a post-parse transformation (no intermediate statement representation)
  #154
• add ASSOCIATE block construct (Fortran 2003 parser only) #165
• CommonGroup AST nodes now store Declarators instead of Expressions
  #173
  • various bug fixes related to their typing as a result
• CI now building on Windows, and save Linux & Windows executables for each
  build
• various bugfixes (#34, #155)