add verbosity option to each model class

[dswah]

• [X] all GAM classes have a verbose argument. this makes them compatible with sklearn GridsearchCV + RandomizedsearchCV

[codecov[bot]]

Codecov Report

Merging #181 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #181   +/-   ##
=======================================
  Coverage   91.58%   91.58%           
=======================================
  Files          19       19           
  Lines        2364     2364           
=======================================
  Hits         2165     2165           
  Misses        199      199

Impacted Files	Coverage Δ
pygam/pygam.py	89.45% <ø> (ø)	:arrow_up:

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