Expose ppline in Alignment class

[arajkovic]

Hi!

This PR exposes the ppline string from P7_ALIDISPLAY.
We're using pyhmmer here at EBI for the new version of the HMMER web tool. While working on the alignment display, I realised that the posterior probability annotation (ppline) is missing, so adding it to the Alignment class.

Cheers!

[althonos]

Would you mind naming it posterior_probabilities instead of ppline, to be a bit more informative on the Python side? Thanks for the PR 😄

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (149785c) 79.59% compared to head (ec8d6d8) 79.60%.
Report is 1 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #59   +/-   ##
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  Coverage   79.59%   79.60%           
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  Files           7        7           
  Lines        7008     7010    +2     
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+ Hits         5578     5580    +2     
  Misses       1430     1430           

Flag	Coverage Δ
v3.10	79.60% <100.00%> (+<0.01%)	⬆️
v3.11	79.60% <100.00%> (+<0.01%)	⬆️
v3.12	79.60% <100.00%> (+<0.01%)	⬆️
v3.7	79.57% <100.00%> (+<0.01%)	⬆️
v3.8	79.60% <100.00%> (+<0.01%)	⬆️
v3.9	79.60% <100.00%> (+<0.01%)	⬆️

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[althonos]

Thanks! I'll make a new release shortly.