improve docs, tests, coverage

[codecov-commenter]

Codecov Report

Base: 82.64% // Head: 90.61% // Increases project coverage by +7.96% :tada:

Coverage data is based on head (d120e10) compared to base (a550fc7). Patch coverage: 87.50% of modified lines in pull request are covered.

:exclamation: Current head d120e10 differs from pull request most recent head 43cfbfc. Consider uploading reports for the commit 43cfbfc to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #105 +/- ## ========================================== + Coverage 82.64% 90.61% +7.96% ========================================== Files 5 5 Lines 484 490 +6 ========================================== + Hits 400 444 +44 + Misses 84 46 -38 ``` | [Impacted Files](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate) | Coverage Δ | | |---|---|---| | [src/IndividualDisplacements.jl](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate#diff-c3JjL0luZGl2aWR1YWxEaXNwbGFjZW1lbnRzLmps) | `50.00% <ø> (ø)` | | | [src/compute.jl](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate#diff-c3JjL2NvbXB1dGUuamw=) | `93.60% <ø> (+5.63%)` | :arrow_up: | | [src/API.jl](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate#diff-c3JjL0FQSS5qbA==) | `88.26% <50.00%> (-8.10%)` | :arrow_down: | | [src/data\_wrangling.jl](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate#diff-c3JjL2RhdGFfd3JhbmdsaW5nLmps) | `91.36% <100.00%> (+29.36%)` | :arrow_up: | | [src/toy\_models.jl](https://codecov.io/gh/JuliaClimate/IndividualDisplacements.jl/pull/105/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate#diff-c3JjL3RveV9tb2RlbHMuamw=) | `93.02% <100.00%> (+2.39%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaClimate)

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