Add solcOptimizerDetails option

[cgewecke]

Resolves: #675, #636 to the extent possible by adding ability to custom configure solc optimizer details and some README info about this issue.

[codecov-commenter]

Codecov Report

Merging #683 (1ca6b42) into master (5b7eb34) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #683   +/-   ##
=======================================
  Coverage   98.69%   98.70%           
=======================================
  Files          22       22           
  Lines         996     1000    +4     
=======================================
+ Hits          983      987    +4     
  Misses         13       13           

Impacted Files	Coverage Δ
lib/api.js	100.00% <100.00%> (ø)
plugins/hardhat.plugin.js	93.87% <100.00%> (+0.19%)	⬆️

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