Add blacklight configuration for registering additional response formats...

[cbeer]

... for the #index action

Options include:

• do the default

    config.index.respond_to.yaml = true

• don't render the format

    config.index.respond_to.yaml = true

• options for render

    config.index.respond_to.yaml = { layout: 'custom-layout' }

• custom proc to render

    config.index.respond_to.yaml = lambda { render text: "stuff" }

• controller method to render

    config.index.respond_to.yaml = :my_custom_yaml_serialization

[jcoyne]

@cbeer Do you want to cut a 5.0.2 before I merge these commits targeting 5.1.0?

[cbeer]

I think that's a good idea. At least until having them open blocks immediate work (at which point, it's worth cutting a release-5.0 branch and backporting changes from master, I suppose)

[coveralls]

Coverage remained the same when pulling 4dd0ff6 on index-response-formats into d1a9955 on master.

[cbeer]

12:01 ] jcoyne> cbeer: what's the use case for blacklight #761
12:01 ] jcoyne> why would I want to add a response proc in the config?
12:02 ] cbeer> jcoyne: i don't know about the proc (it was just convenient), but the use case for #761 in general is:
12:02 ] cbeer> in the blacklight-table plugin (or, the blacklight-map plugin, or something else), i need a way to inject different response types for the #index action without overriding the #index action.
12:03 ] cbeer> so, for blacklight-table, it makes sense (to me, at least) to add a csv output (which i think should play nice with some of the js table-displaying infinite scrolling widgets)