Add methods similar to PostGIS's ST_DumpPoints function.

This method dumps out the points of a geometry into an Array. The Array
might be multi-dimensional, such as in the case of Polygons for the
exterior and interior rings or for collections like MultiLineStrings.
Add methods for getting maximum and minimum x, y and z values.
Add a snap_to_grid method on everything.

Based on the PostGIS ST_SnapToGrid function.
Add geometry transformations, like rotate, scale, etc.

Based on the PostGIS transformation functions.
Add a Geos::LineString#line_interpolate_point method.

Based on the PostGIS ST_Line_Interpolate_Point function.
Rework some tests for the sake of consistency.
Move this code into a helper function.
Add Geos::LinearRing#to_line_string, Geos::LineString#to_linear_ring, #to_polygon.