As pointed out by the linter, some exported functions and types are
missing doc comments.
The linter warnings have been reduced from 194 to 116.
Not all missing comments have been added in this commit though.
This change is motivated by Netlify's `_redirects` files, which is currently not possible to generate with Hugo.
This commit adds a `Delimiter` field to media type, which defaults to ".", but can be blanked out.
Fixes#3614
This commit also adds a new command, docshelper, with some utility funcs that adds a JSON datafiles to /docs/data that would be a pain to create and maintain by hand.
Fixes#3242
