Value is overrated

Modify and fix NT2/Boost.SIMD so the value() fonction is not required anymore. It was 99% useless after the change makign sequence and fusion sequence automatically handled by tests but it was still lingering n various places. It is now removed and the protocol to handle primitive-like type is to go through the a more classical .value() extension point on said types.
https://github.com/MetaScale/nt2/commit/a8a4e96a4d8bc5c31f29e750b5f198677a99d2b2#diff-9

Is what was done for that. Is it OK ?