start of narrow_types!() pull request using lazy eval

[anandijain]

Attempt at solving #9

I think adding a test or example will be important, as well as dealing with the fact that the x field in NarrowTypes will have an outdated schema. I'm not a huge fan of this, but I suppose that anyone with the intention of creating a NarrowTypes struct, will evaluate and receive just a Table with the narrowed schema.

Would love feedback!

Thanks

This is what I've enumerated as todos

• [ ] example/test
• [ ] docs/explanation of struct
• [ ] specifying columns to narrow

• [ ] row access checking?

[codecov[bot]]

Codecov Report

Merging #11 into master will decrease coverage by 4.19%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #11      +/-   ##
==========================================
- Coverage   94.00%   89.80%   -4.20%     
==========================================
  Files           1        1              
  Lines         150      157       +7     
==========================================
  Hits          141      141              
- Misses          9       16       +7     

Impacted Files	Coverage Δ
src/TableOperations.jl	89.80% <0.00%> (-4.20%)	:arrow_down:

---

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 36109cf...593cd7a. Read the comment docs.

[quinnj]

Rebased and updated in https://github.com/JuliaData/TableOperations.jl/pull/14