Date format supports recent/non-recent format

[manno]

Support newline separator to specify a different date format for recent files.

This is similar to the TIME_STYLE=iso format, however the formats can be freely chosen.
(Also iso can only be set via the env var, not the command line.)

refers to #554

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TODO

• Use cargo fmt
• Add necessary tests
• Add changelog entry

[codecov-commenter]

Codecov Report

Merging #600 (83d0aec) into master (0a3a6f1) will increase coverage by 0.34%.
The diff coverage is 84.21%.

@@            Coverage Diff             @@
##           master     #600      +/-   ##
==========================================
+ Coverage   85.89%   86.23%   +0.34%     
==========================================
  Files          37       37              
  Lines        3849     3996     +147     
==========================================
+ Hits         3306     3446     +140     
- Misses        543      550       +7     

Impacted Files	Coverage Δ
src/app.rs	72.46% <59.09%> (-0.12%)	⬇️
src/meta/date.rs	99.41% <100.00%> (+0.86%)	⬆️
src/color.rs	49.14% <0.00%> (-2.05%)	⬇️
src/display.rs	75.00% <0.00%> (-0.41%)	⬇️
src/meta/size.rs	95.40% <0.00%> (ø)
src/icon.rs	97.68% <0.00%> (+0.02%)	⬆️
src/sort.rs	98.26% <0.00%> (+0.32%)	⬆️
src/meta/name.rs	92.88% <0.00%> (+0.44%)	⬆️
src/flags/sorting.rs	99.13% <0.00%> (+0.54%)	⬆️
... and 1 more

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[manno]

newline='
'
lsd -l --date "+%h %d %H:%M$newline%h %d %Y"

[manno]

I'm new to Rust, let me know if something is off about this PR.
Should I also update the documentation?

[meain]

Sorry for the late response, I was a bit occupied. Just a few suggestions on the PR. Also we could add this info to the man pages (probably also mention the TIME_STYLE env variable).

[manno]

I rebased and added information to the README and Changelog.