Update estim

[pw0908]

Adds a few new features:

• export_model: exports all the model parameters to a CSV. Useful for exporting results from parameter estimation.
• Add option to define your own objective function using the objective_form optional argument.
• Add extension for Metaheuristics.jl to abstract away complexities with parameter estimation.

[codecov]

Codecov Report

Merging #211 (31038b8) into master (37d9a0f) will decrease coverage by 0.27%.
Report is 3 commits behind head on master.
The diff coverage is 66.22%.

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
- Coverage   82.12%   81.85%   -0.27%     
==========================================
  Files         261      264       +3     
  Lines       16789    17082     +293     
==========================================
+ Hits        13788    13983     +195     
- Misses       3001     3099      +98     

Files	Coverage Δ
src/Clapeyron.jl	100.00% <ø> (ø)
src/base/EoSModel.jl	79.16% <100.00%> (+0.29%)	⬆️
src/database/UserReader.jl	84.00% <100.00%> (ø)
src/database/database_utils.jl	60.30% <0.00%> (-0.31%)	⬇️
src/database/database.jl	86.59% <25.00%> (-0.60%)	⬇️
src/estimation/estimation.jl	53.09% <57.14%> (+0.24%)	⬆️
src/utils/export_model.jl	97.46% <97.46%> (ø)
ext/ClapeyronMetaheuristicsExt.jl	0.00% <0.00%> (ø)
src/database/database_writer.jl	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes