Add logkernel, stieltjes, and powerkernel functions

[dlfivefifty]

No description provided.

[codecov]

Codecov Report

Patch coverage: 90.82% and project coverage change: +4.74 🎉

Comparison is base (978595d) 89.02% compared to head (aae1549) 93.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   89.02%   93.76%   +4.74%     
==========================================
  Files           5        5              
  Lines         337      321      -16     
==========================================
+ Hits          300      301       +1     
+ Misses         37       20      -17     

Impacted Files	Coverage Δ
src/SingularIntegrals.jl	33.33% <ø> (ø)
src/power.jl	96.42% <88.88%> (+2.88%)	⬆️
src/logkernel.jl	92.72% <89.47%> (+5.42%)	⬆️
src/stieltjes.jl	94.28% <91.93%> (+8.07%)	⬆️

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