Invalid zoneNum for longitude = 180

[shonji-slm]

Appears it's been 5 years or so since this code was last touched. In the case it's still being maintained...

• latLonToZone() returns either zone 1 and 61 for longitudes -180 and 180, respectively. It should return zone 1 for both values.
• the easting returned from fromLatLong() depends on the current behavior of latLonToZone(); fixing the latter breaks the former.

Thanks ;)