Support style dictionary

[banesullivan]

Resolves #730

I changed a few tests at random to use a dict instead of doing json.dumps to make sure this is tested

[manthey]

My one concern is with tile source caching. Currently, the style parameter is used for caching -- if the dictionary is identical enough, then it works as expected, but if the style dictionary differs, the caching may be less than expected (e.g., have equivalent dictionaries whose keys are differently ordered). I'm wondering if it would be worth LRU hashing function so that if style is a dictionary it is serialized to json with sorted keys rather than just used as a python repr.

Or, maybe we don't care about efficiency in that case because a client is unlikely to reorder a style dictionary between tile source accesses.

[banesullivan]

Or, maybe we don't care about efficiency in that case because a client is unlikely to reorder a style dictionary between tile source accesses.

I think it's an unlikely edge case that the dictionary keys will be differently ordered between requests

(e.g., have equivalent dictionaries whose keys are differently ordered). I'm wondering if it would be worth LRU hashing function so that if style is a dictionary it is serialized to json with sorted keys rather than just used as a python repr.

Should we just convert the dict to an OrderedDict?: https://docs.python.org/3/library/collections.html#collections.OrderedDict

and perhaps also sort the JSON blob as well?

[manthey]

When we generate the JSON blob from the dict, we are ordering it. As of Python 3.6, all dictionaries are ordered . I think I'll merge this -- if anyone ever mutates the order of the keys in the dict and notices caching misses, we'll handle it then.