Add direct geospatial index support

[benargo]

Since #371 was raised back in 2014 I’ve wanted a way to improve and simplify adding geospatial indexes.

For a long time now I've been returning to that issue as a basic guide on how to implement geospatial queries.

There's plenty of other issues out there about how to use geospatial features.

This pull request adds geospatial support by adding a geospatial index function to the Schema builder, and updating the documentation to help others how this can be done.

Affected issues

• Question: geoNear command. #55
• Geo near #297
• Can't canonicalize query: BadValue $geometry is required for geo near query #299
• Storing Geodata #371
• query change - lat long  #708
• $near operator is not working #853
• Use where condition in Laravel MongoDB along with GeoSpatial whereRaw function #886
• Problems using $geoNear #965

[arubacao]

@benargo thanks for the great contribution

[jenssegers]

Thanks @benargo! 🍺