Add support for chrono::Duration

[jonasbb]

Part of #56

[codecov]

Codecov Report

Merging #104 into master will increase coverage by 1.79%.
The diff coverage is 91.75%.

@@            Coverage Diff             @@
##           master     #104      +/-   ##
==========================================
+ Coverage   77.75%   79.55%   +1.79%     
==========================================
  Files          23       23              
  Lines        1241     1423     +182     
==========================================
+ Hits          965     1132     +167     
- Misses        276      291      +15     

Impacted Files	Coverage Δ
src/chrono.rs	73.93% <85.43%> (+19.10%)	⬆️
tests/chrono.rs	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e776acb...78b72f7. Read the comment docs.

[jonasbb]

bors r+

[bors]

Build succeeded:

• Build and Test (ubuntu-latest, 1.36.0)
• Build and Test (ubuntu-latest, beta)
• Build and Test (ubuntu-latest, nightly)
• Build and Test (ubuntu-latest, stable)
• Build and Test (windows-latest, 1.36.0)
• Build and Test (windows-latest, beta)
• Build and Test (windows-latest, nightly)
• Build and Test (windows-latest, stable)
• clippy "All Features" (ubuntu-latest / nightly)
• clippy "All Features" (ubuntu-latest / stable)
• clippy "All Features" (windows-latest / nightly)
• clippy "All Features" (windows-latest / stable)
• clippy "Default" (ubuntu-latest / nightly)
• clippy "Default" (ubuntu-latest / stable)
• clippy "Default" (windows-latest / nightly)
• clippy "Default" (windows-latest / stable)
• clippy "No Default Features" (ubuntu-latest / nightly)
• clippy "No Default Features" (ubuntu-latest / stable)
• clippy "No Default Features" (windows-latest / nightly)
• clippy "No Default Features" (windows-latest / stable)
• Rustfmt (stable)

[Stargateur]

Some doc would be nice

[jonasbb]

I did not manage to document the new code sufficiently, but it is on my agenda. Contributions are welcome too :)

[jonasbb]

@Stargateur I added some documentation for DurationSections and DurationSectionsWithFrac in #153. This is available in master now. I plan on putting out a new preview version soon too.