2.0.3

• Add subclass of ManifestStaticFilesStorage. Thank to @jhpinson
• Change the documentation to use PipelineManifestStorage in configuration
  instead of PipelineCachedStorage now deprecated.
• Change import MutableMapping from collections.abc. Thank to @colons
• Fix Middleware to properly decode HTML. Thank to @gatsinski
• Keep mimetypes as str. Thank to @benspaulding
• Based on #642 add 'NonPackagingPipelineManifestStorage' and update
  the documentation: storages.rst. Thank to @kronion
• Remove futures from pipeline setup.py requirements.