Support 32bit Linux builds

[breznak]

This feature was removed, but as we got rid of all ASM, it might be feasible to turn it on easily again.

• see of 32bit linux can compile
• set-up ENV_MATRIX in Travis CI

https://discourse.numenta.org/t/running-nupic-on-arm-platforms-non-raspberry-solution/2715

[breznak]

Bump since we now use cibuildwheel CIBW to automatically build wheels on manylinux2014 image.
There are still some bugs in 32bit i686 code, but this is feasible.

[breznak]

@paulscode our CI build is now much better, will you have time to investigate this?