refactor: introduce text search type

Created by: rvantonder

Removes the type Args definition (search.Args everywhere) and places the search.Args fields as members in the type search.TextParameters. The content of type Args are removed in args.go and placed in types.go. All uses are updated.

I want to reiterate: I'm not overly attached to type names here, I just want to be consistent and explicit with respect to things in types.go for the more significant changes. We can rename these things wholesale in an easy way according to taste later (if there's a consensus on something like Args, or Params or whatnot). I promise.