Add all data samples provided in R and update load_data

[iuliadmtru]

load_data now works for general file names. I added all the datasets provided by the R package, downloaded from here: https://github.com/cran/survey/tree/master/data and converted to CSV.

[ayushpatnaikgit]

We also need a separate documentation file, perhaps called “Sample datasets”.
This should contain documentation about all the sample datasets.

[ayushpatnaikgit]

Perhaps, we should

1. Change the name of the folder from assets to sample_datasets. This seems apt since we are reading all the .csv files from the folder, and that means we won't have another other kinds of assets.
2. Change the filename containing the load_dataset function from example.jl to sample_datasets.jl or load_datasets.jl.

@greimel what do you think?

[codecov-commenter]

Codecov Report

Merging #35 (d7822ae) into main (f4dc08f) will increase coverage by 0.42%.
The diff coverage is 100.00%.

❗ Current head d7822ae differs from pull request most recent head 0653787. Consider uploading reports for the commit 0653787 to get more accurate results

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   65.82%   66.25%   +0.42%     
==========================================
  Files           8        8              
  Lines         158      160       +2     
==========================================
+ Hits          104      106       +2     
  Misses         54       54              

Impacted Files	Coverage Δ
src/example.jl	100.00% <100.00%> (ø)

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[greimel]

Have you checked that it is permitted to make these files available here?

[ayushpatnaikgit]

Have you checked that it is permitted to make these files available here?

Should be fine since we are using the same license as the R package that contains these files. But I'll verify this with Thomas Lumley.

[ayushpatnaikgit]

Perhaps, we should

1. Change the name of the folder from `assets` to `sample_datasets`. This seems apt since we are reading all the `.csv` files from the folder, and that means we won't have another other kinds of assets.

2. Change the filename containing the `load_dataset` function from `example.jl` to `sample_datasets.jl` or `load_datasets.jl`.

@greimel what do you think?

@iuliadmtru can you make these changes in a new PR?