Add the query_url method

[EdgarOrtegaRamirez]

Closes #38 (Expose a method that turns parameters into a query URL)

Overview

Expose a method that turns parameters into a query URL, so the URL could be used to query asynchronously or from another HTTP library or system.

Solution

Add a query_url method that generates a URL for a query without running it, and allow the query method to be a consumer of this one.

Keen.query_url('users', {analysis_type: 'count'})
# https://api.keen.io/3.0/projects/12345/queries/count?event_collection=users

[joshed-io]

Very cool!

Here are a few requests to take care of before we merge this in:

• Can we make it so query is a consumer of query_url? It feels like that's the right pattern - query_url should handle making the string and query should just be doing the HTTP work.
• Can we avoid using any instance or self.* variables? The client is designed to be stateless and so any instance variables could bleed between query calls.
• Can you remove any of the whitespace and other refactoring diffs from the PR? It would be awesome to have those, but for the sake of readability and avoiding regressions I'd like to process them separately.
• Can you add tests for missing project id / api key in query_url?

Really appreciate the PR, I think this'll be a popular feature!

[EdgarOrtegaRamirez]

@dzello I just updated the PR, please take a look.

[joshed-io]

Looks great, thanks!