Allow conditionally hidden fields

[protestContest]

The hidden/0 view callback is handy to remove sensitive fields in views. In some cases, an API may want to hide certain fields by default, but show them in some cases (in my application's case, some fields should be visible if specifically requested as part of a sparse fieldset).

It would be handy if the hidden callback accepted conn as an argument, so the application could decide what fields to hide for a particular request.

Any thoughts on this? I'm happy to open a PR for the change.

Related issue: #68

[mattpolzin]

that sounds like a reasonable solution as long as you don't need to omit any relationships (really, anything outside of attributes) conditionally. just cuz the hidden/0 function only operates on fields to begin with.