[ENH] Add hexagonal ElectrodeGrid (#160)
[ENH] Add hexagonal ElectrodeGrid (#160)

* Add hexagonal ElectrodeGrid class to implants.base

* Update documentation for ElectrodeGrid

Co-authored-by: Michael Beyeler <c39c93bb4a0bed84801bde1cdcc4336f26e3fee7@users.noreply.github.com>
uwescience/pulse2percept,uwescience/pulse2percept,uwescience/pulse2percept,mbeyeler/pulse2percept