0.4.1

Changes

• Added core rule conventions that checks for the Conventionsattribute.
• Added core rule context-descr that checks content description
• Added core rule var-descr that checks data variable description
• Renamed rules for consistency:
  • var-units-attrs and var-units
  • flags into var-flags

Fixes

• Fixed an issue that prevented recursively traversing folders referred
  to by URLs (such as s3://<bucket>/<path>/) rather than local directory
  paths. (#39)