Fix days to hours boundary for precise delta

[eldipa]

Fixes #14

Changes proposed in this pull request:

• Propagate correctly the days to hours in precisedelta
• Propose a truncate flag to truncate and remove values too close to zero in precisedelta

Note: I don't feel that truncate is the correct name and I think that it could be easily misinterpreted. We need a better name.
This PR also does not include a documentation for this flag nor tests (but a file in tests/issue-14-days-hours-boundary-in-precisedelta.md describes and tests all the cases discussed in #14 so it can be used as the base for an unit test and/or as the tests themselves running them with byexample )

Closes #14

[codecov-commenter]

Codecov Report

Merging #19 (6cef97b) into main (410b51d) will decrease coverage by 2.13%.
The diff coverage is 30.00%.

❗ Current head 6cef97b differs from pull request most recent head cf7ec9d. Consider uploading reports for the commit cf7ec9d to get more accurate results

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   99.68%   97.54%   -2.14%     
==========================================
  Files           9        9              
  Lines         635      653      +18     
==========================================
+ Hits          633      637       +4     
- Misses          2       16      +14     

Flag	Coverage Δ
macos-latest	96.32% <30.00%> (-2.11%)	⬇️
ubuntu-latest	96.32% <30.00%> (-2.11%)	⬇️
windows-latest	96.01% <30.00%> (-2.10%)	⬇️

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Impacted Files	Coverage Δ
src/humanize/time.py	93.91% <30.00%> (-6.09%)	⬇️

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