6.0.0 beta New SCSS parser

• New SCSS parser using the official SASS parser.
  • Better auto-detection of SCSS variables and mixin parameters.
  • No more scanning of directories for CSS files, only for SCSS and JS files.
• Auto-detected version data for parameters, listing of methods with
  new parameters on API docs index page (Issue #480)
• New --guides-toc-level option to allow multiple levels of headings
  in guide table of contents (Issue #488).
• Default list of external classes now only includes the core
  JavaScript classes. But one can use special syntax
  --external=@browser to automatically define all standard browser
  API classes like HTMLElement and XMLHttpRequest as externals.
• Large refactoring of command line options parsing:
  • Most boolean options are now in --[no-]opt style.
  • Allow comma-separated paths for --tags, --images, --exclude.
• The tag warning type can now be parameterized to ignore warnings
  about particular tags (Issue #500)
• A new @class_icon field for custom tags to allow overriding the icon
  of a class. (Issue #456)
• New @component tag (mostly for internal use).
• Fix crash when parentless sub-cfg in class doc-comment. (Issue #475)
• Fix incompatible encodings error in RKellyAdapter. (Issue #491)
• Fix crash when method inherits from cfg. (Issue #494)
• Eliminate the defunct cat_old_format warning type.