Log-normal log-likelihood

[ben18785]

Adds a log-normal distribution both without (default) and with mean-adjustment as described in #1376

[codecov[bot]]

Codecov Report

Merging #1378 (c69a748) into master (2afaee9) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1378   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           95        95           
  Lines         9282      9321   +39     
=========================================
+ Hits          9282      9321   +39     

Impacted Files	Coverage Δ
pints/__init__.py	100.00% <ø> (ø)
pints/_log_likelihoods.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[MichaelClerx]

@ben18785 @DavAug this is approved. Want to merge it in now?