Implement sampling in C++

[davidchall]

Fixes #12

50-100x faster, 10x less memory allocated

[codecov]

Codecov Report

Merging #19 into master will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   99.06%   99.16%   +0.10%     
==========================================
  Files          24       25       +1     
  Lines        1174     1198      +24     
==========================================
+ Hits         1163     1188      +25     
+ Misses         11       10       -1     

Impacted Files	Coverage Δ
src/IpNetworkVector.h	100.00% <ø> (ø)
R/sample.R	95.65% <100.00%> (+0.65%)	⬆️
src/IpNetworkVector.cpp	100.00% <100.00%> (ø)
src/sample.h	100.00% <100.00%> (ø)
src/wrapper.cpp	100.00% <100.00%> (ø)

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