Remove RasterHistogram module as it now has its own package

[jbisits]

Closes #34, package now does what it says..
Closes #69

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +8.25% 🎉

Comparison is base (2abf4f6) 91.74% compared to head (0a6388a) 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #70      +/-   ##
===========================================
+ Coverage   91.74%   100.00%   +8.25%     
===========================================
  Files           3         7       +4     
  Lines         303       123     -180     
===========================================
- Hits          278       123     -155     
+ Misses         25         0      -25     

Files Changed	Coverage Δ
src/OceanRasterConversions.jl	100.00% <ø> (ø)
src/oceanvariableconversions.jl	100.00% <ø> (ø)
src/alphaandbeta.jl	100.00% <100.00%> (ø)
src/seawaterdensity.jl	100.00% <100.00%> (ø)
src/sp_to_sa.jl	100.00% <100.00%> (ø)
src/theta_to_Theta.jl	100.00% <100.00%> (ø)
src/z_to_p.jl	100.00% <100.00%> (ø)

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