add geohashBase4 method as issue #30

[ppKrauss]

main change was from if (bits === 5) to if (bits === maxBits).

[sunng87]

By making a new encodeBase4, I don't want to change the signature of current encode for bringing in incompatible change.

I suggest to refactoring the code to support base4 encoding.

Also please add the space between operators. And add {} to of else for consistency of coding style.

[ppKrauss]

By making a new encodeBase4, I don't want to change the signature of current encode for bringing in incompatible change.

I not see "default undefined" as a incompatible change.

I suggest to refactoring the code to support base4 encoding.

... Better you do what you whant...

Also please add the space between operators. And add {} to of else for consistency of coding style.

OK. (I think it is possible to enforce style with travis.yml)

[ppKrauss]

Hi, some news here?