Fixes #47. Previously, the near() builder method was used to support the geoNear command instead of $near query criteria. This was unintuitive, given how other geo methods like withinBox() operated.
Instead, we add a new geoNear() builder method, which operates similarly to mapReduce() and switches the query into GEO_LOCATION mode. We also add methods to specify the distanceMultipler and maxDistance options.
The near() builder method is repurposed to define $near query criteria for a field or expression.