lib/Geo/GoogleMaps/OffsetCenter.pm: Purge old method

Remove offset_center_by_occlusion in favor of offset_center_by_pixel. Might
bring it back as an interface to the pixel method. It's just more generic.
lib/Geo/GoogleMaps/OffsetCenter.pm: 6 decimal places ought to be enough for everyone...

It's actually arguably more than is necessary for Google Maps needs.

It yields a precision that can address 10s of centimeters, that's very precise
for GPS uses.
t/functional.t: Basic test case
Bump Version Number
Changes: v0.04