Automatic column remapping

[billdenney]

This pull request addresses #97 and allows $INPUT records like:

$INPUT ID=FOO AMT=BAR DV

Where the output $TABLEs have remapped the ID column to FOO.

[codecov]

Codecov Report

Merging #100 into master will decrease coverage by 1.45%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
- Coverage   95.91%   94.45%   -1.46%     
==========================================
  Files          40       41       +1     
  Lines        3327     3086     -241     
==========================================
- Hits         3191     2915     -276     
- Misses        136      171      +35

Impacted Files	Coverage Δ
R/xpose_data.R	98.48% <100%> (-1.52%)	⬇️
R/read_nm_tables.R	92.53% <86.36%> (-1.88%)	⬇️
R/parse_nm_input_record.R	97.43% <97.43%> (ø)
R/print_xpose_plot.R	84.14% <0%> (-4.43%)	⬇️
R/vpc_data.R	85.03% <0%> (-4.4%)	⬇️
R/xplot_helpers.R	95.34% <0%> (-3.96%)	⬇️
R/vpc_helpers.R	91.04% <0%> (-3.9%)	⬇️
R/utils.R	96.15% <0%> (-3.85%)	⬇️
R/xplot_qq.R	92.85% <0%> (-3.81%)	⬇️
R/xplot_distrib.R	91.93% <0%> (-3.66%)	⬇️
... and 26 more

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