Implementing ColSpec interface in Select and Reject

[eliascarv]

To implement the ColSpec interface, the following steps must be performed:
1 - add colspec fied:

struct MyTransform{S<:ColSpec,#= other type params =#}
  colspec::S
  # other fileds
end

2 - using _filter(colspec, cols) internal function:

function apply(transform::MyTransform, table)
  allcols = Tables.columnnames(table)
  # selected columns
  cols = _filter(transform.colspec, allcols)
  # code...
end

[codecov-commenter]

Codecov Report

Merging #31 (08909ba) into master (fcf126b) will decrease coverage by 0.39%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
- Coverage   92.73%   92.34%   -0.40%     
==========================================
  Files          16       16              
  Lines         413      405       -8     
==========================================
- Hits          383      374       -9     
- Misses         30       31       +1     

Impacted Files	Coverage Δ
src/transforms/colspec.jl	100.00% <ø> (ø)
src/transforms/select.jl	91.30% <90.90%> (-2.21%)	⬇️
src/transforms/filter.jl	100.00% <100.00%> (ø)

---

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 fcf126b...08909ba. Read the comment docs.