Implement/test columnar geospatial

[randyzwitch]

Implement TColumn for geospatial types, so that data can be loaded using load_table_binary_columnar

[codecov[bot]]

Codecov Report

Merging #75 into master will decrease coverage by 0.1%. The diff coverage is 91.6%.

@@           Coverage Diff            @@
##           master     #75     +/-   ##
========================================
- Coverage    23.9%   23.8%   -0.2%     
========================================
  Files          11      11             
  Lines        2561    2557      -4     
========================================
- Hits          614     609      -5     
- Misses       1947    1948      +1

Impacted Files	Coverage Δ
src/constructors.jl	95.3% <91.6%> (-1.1%)	:arrow_down:

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[randyzwitch]

Work towards #41