Add VecSkipError<T> de behavior

[hdhoang]

hi! This implements #321

I will added doctest & motivating example based on the SO question.

I'm not sure if this should go into the rust module. I'm also confused about the T and U parameter names on SerializeAs impl, which one should go on VecSkipError.

Hope this helped

[jonasbb]

Hi, thank you for the PR. I left you some notes on the individual parts. Maybe you could also add a tiny snippet to serde_with/src/guide/serde_as_transformations.md That file contains all the available transformations this crate provides.

[codecov]

Codecov Report

Merging #383 (3be4743) into master (0243453) will decrease coverage by 0.28%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #383      +/-   ##
==========================================
- Coverage   75.43%   75.15%   -0.29%     
==========================================
  Files          47       47              
  Lines        2842     2858      +16     
==========================================
+ Hits         2144     2148       +4     
- Misses        698      710      +12     

Impacted Files	Coverage Δ
serde_with/src/lib.rs	75.00% <ø> (ø)
serde_with/src/de/impls.rs	72.41% <66.66%> (-0.32%)	⬇️
serde_with/src/ser/impls.rs	93.75% <100.00%> (+0.11%)	⬆️
serde_with/tests/serde_as/lib.rs	100.00% <100.00%> (ø)
serde_with/tests/derives/deserialize_fromstr.rs	84.00% <0.00%> (-16.00%)	⬇️
...e_with/src/duplicate_key_impls/first_value_wins.rs	50.00% <0.00%> (-11.54%)	⬇️
...de_with/src/duplicate_key_impls/last_value_wins.rs	90.00% <0.00%> (-10.00%)	⬇️
...with/src/duplicate_key_impls/error_on_duplicate.rs	90.00% <0.00%> (-10.00%)	⬇️
serde_with/src/utils.rs	87.87% <0.00%> (-6.07%)	⬇️
serde_with/src/utils/duration.rs	87.79% <0.00%> (-0.65%)	⬇️
... and 1 more

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[jonasbb]

Thanks for working on this. I updated the documentation in serde_as_transformations.md a bit. The rest looks good.

[jonasbb]

bors merge

[bors]

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