Decide on what's part of OceanParameterizations.jl and what should be in a script

[ali-ramadhan]

I think I didn't organize the repo well since src/ includes stuff like https://github.com/CliMA/OceanParameterizations.jl/blob/master/src/ocean_convection.jl which now seems pretty specific to free convection so it shouldn't have been in src/.

Things like https://github.com/CliMA/OceanParameterizations.jl/blob/master/src/GaussianProcesses/GaussianProcesses.jl and https://github.com/CliMA/OceanParameterizations.jl/blob/master/src/differentiation_operators.jl are more generally useful so they might belong in src/.

Solving this issue would probably help a lot with #24.

[ali-ramadhan]

Maybe what I should have done is create a FreeConvection module with my scripts so it's separate from OceanParameterizations.jl then move any generally useful bits/utils into OceanParameterizations.