Expand JS API CKAN data loader to accept multiple filters before requesting

[NightJar]

As part of the work in #69 @ScopeyNZ has introduced a simple "vanilla" JS (read: framework agnostic) wrapper for requesting data from a CKAN API given a few configuration options.

At current it appears to not support the addition of multiple filters before launching the request - which is a problem in the front-end for an end-user wishing to add multiple filters for a resource they're attempting to inspect.

In order to supply the ability for an end-user to search/filter and fulfill requisites for #4, #5, & #8 this will need to be expanded to allow for multiple filters. It will also in part tidy off #1 by providing front end authors a more complete API to build their own interfaces with (in a customisation case).

The resulting JS API should be easy to consume, and also support searching all fields with a single value (or a single value for multiple fields).