Allow location nans

[jeromekelleher]

Also updates for version 0.2.2

[codecov]

Codecov Report

Merging #352 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #352      +/-   ##
==========================================
- Coverage   86.48%   86.48%   -0.01%     
==========================================
  Files          20       20              
  Lines       14030    14024       -6     
  Branches     2742     2740       -2     
==========================================
- Hits        12134    12128       -6     
  Misses        977      977              
  Partials      919      919

Flag	Coverage Δ
#c_tests	87.56% <100%> (-0.01%)	⬇️
#python_c_tests	90.31% <100%> (ø)	⬆️
#python_tests	99.24% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
c/tskit/core.c	81.6% <ø> (-0.14%)	⬇️
c/tskit/tables.c	78.05% <ø> (-0.03%)	⬇️
python/tskit/_version.py	100% <100%> (ø)	⬆️

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