Enable `getproperty` for `Symbol` keys

[andyferris]

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This enables convenient access to dictionaries with Symbol keys. One potential use case is the rows or columns of a table, similar to a dataframe.

[codecov[bot]]

Codecov Report

Merging #43 (80a2f3b) into master (aeab543) will decrease coverage by 0.16%. The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
- Coverage   70.34%   70.18%   -0.17%     
==========================================
  Files          19       19              
  Lines        1703     1707       +4     
==========================================
  Hits         1198     1198              
- Misses        505      509       +4     

Impacted Files	Coverage Δ
src/indexing.jl	53.84% <0.00%> (-3.54%)	:arrow_down:
src/Indices.jl	81.22% <100.00%> (ø)

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[aplavin]

Bump @andyferris :)

[rafaqz]

Seconding the bump on this, a Dictionary with getproperty on keys would be perfect for seamless switching between Dictionary and NamedTuple for runtime/compilation tradeoffs, e.g. in DimensionalData.jl DimStack.