add hyperlinking support for json files

- add support for hyperlinking to file paths in `json` files
- make a common method for file path hyperlinking
- some initial work to resolve `package` relative references when hyperlinking

@umop
Nit.  Maybe 
`new RegExp(r'^(package:|(.*/)?packages/)(.*)$');` instead of 
`new RegExp(r'^(package:|.*/packages/|packages/)(.*)$');`