Support UPS for polar regions

[marnen]

Right now, if a LatLon with latitude greater than 84 or less than -80 is converted to UTM, the conversion fails with an error that the latitude is out of UTM range. Since UPS is typically used to fill in these gaps, this gem should support the UPS system, and probably consider it to be a part of UTM. (I'll contribute code if I have time, but I don't know if I will.)