Read and maintain column attributes

[jonocarroll]

In reference to #20:

• The label column was attempted to be read, but it doesn't exist
• The attributes were stripped on type conversion

This resolves the current check failure (12 pass, 0 fail) and restores check to 0 | 0 | 0 status.

[codecov-io]

Codecov Report

Merging #21 into master will decrease coverage by 2.25%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #21      +/-   ##
==========================================
- Coverage   77.72%   75.47%   -2.26%     
==========================================
  Files           3        2       -1     
  Lines         229      212      -17     
==========================================
- Hits          178      160      -18     
- Misses         51       52       +1

Impacted Files	Coverage Δ
R/read_csvy.R	69.93% <100%> (-0.54%)	:arrow_down:
R/write_csvy.R	89.83% <0%> (-1.7%)	:arrow_down:
R/get_yaml_header.R

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