add separate assess method; add docs on AlefeldPotra methods

[jverzani]

Add an assess_convergence method for bisection that does not check isinf_f.

Update docs on Alefeld Potra methods about not honoring tolerances on size of f.

Close #457, Close #458

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.38%. Comparing base (95da1f5) to head (8e1899c).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #459      +/-   ##
==========================================
+ Coverage   86.35%   86.38%   +0.03%     
==========================================
  Files          37       37              
  Lines        2440     2446       +6     
==========================================
+ Hits         2107     2113       +6     
  Misses        333      333              

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