Implement SIMD code to quickly compute skippable connections

[althonos]

This PR adds two SIMD implementations (using SSE2 or AVX2) to compute which node pairs can be ignored when scoring connections between dynamic programming nodes. The code supports compile-time and runtime detection of CPU features using the additional cpu_features library.

[codecov]

Codecov Report

Merging #6 (71fb662) into master (9776a9e) will increase coverage by 0.71%.
The diff coverage is 94.94%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
+ Coverage   92.74%   93.46%   +0.71%     
==========================================
  Files           8        9       +1     
  Lines        2123     2294     +171     
==========================================
+ Hits         1969     2144     +175     
+ Misses        154      150       -4     

Flag	Coverage Δ
CPython	93.46% <94.94%> (+0.71%)	⬆️
Linux	93.46% <94.94%> (+0.71%)	⬆️
OSX	92.50% <82.58%> (-0.25%)	⬇️
PyPy	98.37% <100.00%> (+0.29%)	⬆️
Windows	99.77% <100.00%> (+0.04%)	⬆️
v3.5	93.38% <94.85%> (+0.71%)	⬆️
v3.6	93.43% <94.85%> (+0.71%)	⬆️
v3.7	93.43% <94.85%> (+0.71%)	⬆️
v3.8	93.46% <94.94%> (+0.71%)	⬆️
v3.9	93.46% <94.94%> (+0.71%)	⬆️

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Impacted Files	Coverage Δ
pyrodigal/_pyrodigal.pyx	91.95% <91.66%> (+0.69%)	⬆️
pyrodigal/tests/__init__.py	100.00% <100.00%> (ø)
pyrodigal/tests/test_connection_scorer.py	100.00% <100.00%> (ø)
pyrodigal/tests/test_nodes.py	100.00% <100.00%> (ø)

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