[#1534] if mimetype is none then fall back to provided mimetype
[#1571] Add note about custom mimetypes
Merge pull request #1534 from ckan/1534-fix-none-mimetype

Can't download resources with geojson extension
Merge pull request #1571 from ckan/1571-docs-mimetypes-and-tweaks

Add mention about custom mimetypes in docs
[#1350]  Fix typos and add geojson type
Merge branch 'master' into 1350-resource-format-change