Redefine child/dependent input parameters

[Peter-Metz]

This PR redefines the child/dependent input parameters to be more intuitive. Results are unchanged.

Before this PR, the child/dependent inputs were:

• Number of dependents
• Number of children under 13 with eligible child care expenses
• Number of children under 17 for the entire tax year
• Number of qualifying children for EITC

This PR proposes the following child/dependent inputs:

• Number of children under 13
• Number of children from 13 to 16
• Number of children from 17 to 18 AND from 19 to 24 and a full-time student
• Other dependents

I've gotten feedback from multiple people that the current inputs are confusing and that the error messages are not helpful. I am hoping that the new format is clearer. Feedback is welcome

[codecov-io]

Codecov Report

Merging #53 into master will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
+ Coverage   86.71%   86.84%   +0.13%     
==========================================
  Files           3        3              
  Lines         399      403       +4     
==========================================
+ Hits          346      350       +4     
  Misses         53       53              

Impacted Files	Coverage Δ
taxcrunch/cruncher.py	81.04% <100.00%> (+0.31%)	⬆️

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