Remove Epoch, Event, and Spike objects -- to new branch

The first major backwards-incompatible change for neo. This pull request removes the existing scalar types, Epoch, Event, and Spike. It also renames EpochArray to Epoch` andEventArraytoEvent``.

All neo.core unit tests pass. However, as discussed on the mailing list, neo.io maintainers will need to check for failures in their classes and create pull requests for fixes. The unit tests will be in a failing state until then.

This is the same as #164, but it is being submitted to a new branch instead of master.