Add AMT

[nikhilwoodruff]

Adds parameters and variables from AMT in taxcalc.

[MaxGhenis]

Haven't dug into the logic yet

[codecov]

Codecov Report

Merging #344 (a56874a) into master (7fecba6) will increase coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #344      +/-   ##
==========================================
+ Coverage   94.51%   94.67%   +0.15%     
==========================================
  Files          59       59              
  Lines        3428     3510      +82     
  Branches      469      473       +4     
==========================================
+ Hits         3240     3323      +83     
+ Misses        163      162       -1     
  Partials       25       25              

Impacted Files	Coverage Δ
openfisca_us/variables/irs/inputs.py	99.63% <100.00%> (+0.13%)	⬆️
openfisca_us/variables/irs/outputs.py	97.65% <100.00%> (+0.19%)	⬆️

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[nikhilwoodruff]

@MaxGhenis - so it turns out the OpenFisca logic was correct here: because the calcfunctions in taxcalc are not independent of each other, my approach of generating a unit test by feeding the relevant final variables into the function was incorrect. I've added the script generating unit tests, plus ten random (from the CPS, with non-zero outputs) unit tests for AMT.