EEG 64 channel map

[stedy]

Not sure if this is appropriate for this package but someone suggested this grid at geofacet hafen/geofacet#220 and it seems like it could be a better fit here.

[craddm]

Hi,

I've thought about this a bit before (I suggested using geofacet to the author of that issue at some point, and I've written a function that generates a geofacet compatible grid from a set of electrode locations - I'll see about adding that in the next build.

Cheers,
Matt