Support multiple methods for loading a swagger document.

[ashoda]

There are various requests around supporting loading swagger docs by different means.
Current behavior

• Load JSON from a path relative to the application

Requested:

• Load YAML from a path relative to the application
• Load JSON from local file
• JSON string

It'd make sense for us to look at the various request to determine the ideal approach to makes loading a swagger doc a bit more flexible.

My initial thought is to add support for a Hash or a JSON string in addition to what we currently support, which would afford people enough flexibility to decide how they'd like to load the swagger doc.

cc: @gwshaw @jreece1567

[jreece1567]

@ashoda Agreed. I think Apivore should support both YAML and JSON, loaded in all of the requested ways ...

• From a path relative to the application (an HTTP/S path)
• From a local file
• From a string

cc: @gwshaw

[ben-axnick]

@ashoda I have proposed #106 as a solution.

[philsturgeon]

Kinda taken care of in #118 which adds YAML, as it also pulls in #87 which supports local files.