Add compressed cell values

[fverdugo]

No description provided.

[codecov-io]

Codecov Report

Merging #41 into master will decrease coverage by 0.08%.
The diff coverage is 85.5%.

@@            Coverage Diff            @@
##           master     #41      +/-   ##
=========================================
- Coverage   88.48%   88.4%   -0.09%     
=========================================
  Files          56      57       +1     
  Lines        2457    2526      +69     
=========================================
+ Hits         2174    2233      +59     
- Misses        283     293      +10

Impacted Files	Coverage Δ
src/CellValues/CompressedCellValues.jl	85.5% <85.5%> (ø)

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