Expose a GEOSNode interface in the C-API

[strk]

Such function should be used to fully node input linework. It should take an optional "precision" parameter to perform snapping of input vertices and intersection points to a given grid. Such functionality should be very helpful in improving robustness and predictability for clients.

[strk]

Note that JTS has a GeometryNoder? class under the noding/snapround package.

[strk]

This was done with r3593 -- may be improved to use snaprounding when input precision model is fixed.

No precision parameter was added, I think it makes more sense for precision to be handled globally using a geometrie's PrecisionModel?. This in turn will require exposing ways to set the precision model of geometries being constructed...