Kinemetrics EVT data format support.

Added support for the format + tests + reference PDF.
Appending values is pretty inefficient for everything but 3-byte integers. You can pass the length directly to `unpack` (i.e., `length / numbyte`) to get one big chunk. Even more efficient would be NumPy's `from*` functions, which directly give you an `ndarray`.

Three-byte arrays are the problem child, of course, since nobody supports reading them directly. You might be able to do some fancy math with 2- or 4-byte integers, but that might be premature optimization.