default besselh to k=1 like the docs say it does

[oscardssmith]

The docs say besselh(nu, [k=1,] x) so if the user calls a 2 arg version of this, they are asking for k=1.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.71%. Comparing base (ec6c51d) to head (f1427e9).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #118   +/-   ##
=======================================
  Coverage   95.71%   95.71%           
=======================================
  Files          24       24           
  Lines        2382     2383    +1     
=======================================
+ Hits         2280     2281    +1     
  Misses        102      102           

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