Proxied Requests

[ingalls]

I've been working my way through a ton of potential Michigan sources and seeing a common occurrence of the ArcGIS URL being proxied behind a server which appends the auth token server-side before hitting the actual ArcGIS server.

So a traditional ArcGIS URL Like:

http://example.com/arcgis/rest/services/portAddressPoint/FeatureServer/0

Is proxied through another server like:

https://example.com/proxy.ashx?http://example.com/arcgis/rest/services/portAddressPoint/FeatureServer/0

Since the scraper uses the python requests module to add the param: f=json it correctly detects the previous ? and assumes the f=json are additional params and appends &f=json.

the proxy however expects a double ? as it simply pops the second half url and passes it along. This results in a failed query.

This PR adds an optional --proxy arg to the CLI that allows the scraper to handle double args.

[iandees]

I'd like to get the tests fixed and then will merge this. Thanks @ingalls!