MAINT: Refactor SSE2+ detection

[bashtage]

Refactor compiler support for features to follow GCC-like pattern

[pep8speaks]

Hello @bashtage! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-07-04 10:18:24 UTC

[codecov]

Codecov Report

Merging #172 into master will increase coverage by 0.22%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
+ Coverage   94.86%   95.08%   +0.22%     
==========================================
  Files          37       37              
  Lines       10118    10118              
  Branches      151      151              
==========================================
+ Hits         9598     9621      +23     
+ Misses        494      474      -20     
+ Partials       26       23       -3

Impacted Files	Coverage Δ
randomgen/tests/test_direct.py	99.02% <0%> (+0.61%)	⬆️
randomgen/common.pyx	81.2% <0%> (+1.92%)	⬆️
randomgen/tests/test_seed_sequence.py	100% <0%> (+2.08%)	⬆️

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