Add Education Credit HC

[andersonfrailey]

This PR is a continuation of PR #1247 and adds a haircut for education credits. The reason it was not included in #1247 is at the time I was under the impression that education credits could be zeroed out by simply setting LLC_Expense and ETC_pe_Single/Married to zero, but that is not the case.

cc: @MattHJensen @martinholmer

[codecov-io]

Codecov Report

Merging #1252 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1252   +/-   ##
=======================================
  Coverage   99.66%   99.66%           
=======================================
  Files          38       38           
  Lines        2706     2706           
=======================================
  Hits         2697     2697           
  Misses          9        9

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4076f70...0b7abae. Read the comment docs.

[martinholmer]

@andersonfrailey, Thanks for adding an the additional haircut policy parameter in #1252. Looks good, so I'm merging it now.