[pypy-issue] Issue #2814: _pypyjson should use SIMD when available to skip whitespace characters faster (pypy/pypy)

[Omer Katz]

New issue 2814: _pypyjson should use SIMD when available to skip whitespace characters faster
https://bitbucket.org/pypy/pypy/issues/2814/_pypyjson-should-use-simd-when-available

Omer Katz:

RapidJSON has implemented whitespace skipping using a variety of SIMD interstices.
For [SSE 4.2](https://github.com/Tencent/rapidjson/blob/master/include/rapidjson/reader.h#L281),  [SSE 2](https://github.com/Tencent/rapidjson/blob/master/include/rapidjson/reader.h#L332) and [NEON for ARM](https://github.com/Tencent/rapidjson/blob/master/include/rapidjson/reader.h#L417).
We can port these functions to C pretty easily and the license of RapidJSON is MIT so that's allowed.
The challenge is to detect if the user running PyPy has support for such instructions.