Add ToGeohash and FromGeohash operations

[GCHQ77703]

Adds the ngeohash library to the default bundle, which is ~300 lines of code and has no dependencies.

[CLAassistant]

All committers have signed the CLA.

[GCHQ77703]

A geohash is a way of encoding a latitude and longitude into a single, interleaved string. You can set it to have an arbitrary precision. For example, GCHQ is located at gcnrr8j0e0w6 but you can also specify roughly the same place with just the string gcnrr. It is the storage system for coordinates used in Elasticsearch, MongoDB, HBase and Accumulo, as well as various others.

[GCHQ77703]

Just discovered the wonderful fork operation.

[GCHQ77703]

From the formatMacAddress module:

input.toLowerCase().split(/[,\s\r\n]+/);

I'm now unsure whether it's normal to handle a single input and expect the user to split it for us, or whether it's better for us to split it to save the user adding another module. If the latter is true, it is easy enough to just revert 001f3f3.

[n1474335]

Thanks very much, this is great.

On the forking front, it really just depends on the operation. I think in this case it makes sense to split by line without forcing the user to use 'Fork' so I've added that functionality back in.

I also moved these ops into the 'Hashing' category as I think they fit there slightly better than 'Data format'. I also moved them into the Hashing module. I realise it's a small library, but I really don't want to add any more libraries into the Default module if I can possibly avoid it.