Multitrait metadata

[bhaller]

Changes for multitrait metadata. At present this only handles writing of .trees; reading is completely broken on this branch right now. The writing code is also incomplete; metadata for some mutations will be missing (specifically mutations that were removed from haplosomes for reasons other than fixation, and mutations needed for remembered individuals). Caveat lector.

[codecov]

Codecov Report

❌ Patch coverage is 66.23377% with 52 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.69%. Comparing base (e2bd7c6) to head (4306882).
⚠️ Report is 22 commits behind head on multitrait.

Files with missing lines	Patch %	Lines
core/slim_functions.cpp	0.00%	19 Missing ⚠️
core/mutation.cpp	66.66%	18 Missing ⚠️
core/species.h	0.00%	7 Missing ⚠️
core/slim_globals.cpp	54.54%	5 Missing ⚠️
core/haplosome.cpp	0.00%	2 Missing ⚠️
core/mutation_run.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           multitrait     #614      +/-   ##
==============================================
- Coverage       76.72%   76.69%   -0.04%     
==============================================
  Files             116      116              
  Lines           76446    76825     +379     
  Branches        13787    13859      +72     
==============================================
+ Hits            58655    58918     +263     
- Misses          17791    17907     +116     

Files with missing lines	Coverage Δ
core/individual.cpp	61.42% <100.00%> (-0.24%)	⬇️
core/mutation.h	75.00% <ø> (ø)
core/mutation_block.h	95.00% <ø> (ø)
core/population.cpp	69.47% <100.00%> (+0.23%)	⬆️
core/slim_globals.h	57.89% <ø> (ø)
core/species.cpp	63.56% <ø> (+0.54%)	⬆️
core/species_eidos.cpp	69.07% <100.00%> (+0.10%)	⬆️
core/substitution.cpp	48.51% <100.00%> (-1.25%)	⬇️
core/substitution.h	100.00% <ø> (ø)
core/trait.cpp	85.61% <100.00%> (+2.39%)	⬆️
... and 8 more

... and 3 files with indirect coverage changes

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[bhaller]

Reading is fixed, doc is fixed, treeSeqMetadata() is fixed, time to merge.