Encoders' output is incompatible with the C++ SpatialPooler

[mrcslws]

Using the C++ SpatialPooler, calling SpatialPooler.compute(encoder.encode(42)) will quietly do the very wrong thing because it's given a buffer of 8-bit integers and it thinks it's getting a buffer of 32-bit integers. See: https://discourse.numenta.org/t/inconsistency-between-spatialpooler-in-nupic-and-nupic-bindings/1549/10?u=mrcslws

I think this line should be changed to use numpy.uint32: https://github.com/numenta/nupic/blob/6924a904644bbb8cdba6ca7a62050cf8456614f8/src/nupic/encoders/base.py#L30

Anyone who wants encoders to use fewer bits can explicitly use encodeIntoArray. For encode, we should use a default that works with the SpatialPooler.

[breznak]

Related C++ issue numenta/nupic.core-legacy#961