Add dataJson option in geographyConfig

[ramnathv]

This PR allows the use dataJson in geographyConfig to specify a custom topojson file as a string, instead of having to use dataUrl and link to an external file. This is especially useful in generating standalone html files with no dependencies.

[markmarkoh]

Thanks for this, I think this is a good feature to add.

Since topojson is valid JSON, can we ditch the JSON.parse requirement so that a user can send in normal JSON?

In the event they do have just a string representation, they could always do the JSON.parse external to the DataMaps instantiation.

What do you think?

[ramnathv]

Yes. That will work since the JSON.parse can always be done externally. Do you want me to make that change, or you prefer to merge and make it yourself?

[markmarkoh]

I'd prefer you make the change and push back to this PR.

[ramnathv]

I have made the change.