Add Epoch::from_ptp_*

[georgeboot]

This pull requests adds the Epoch::from_ptp_seconds and Epoch::from_ptp_milliseconds helper methods to deal with IEEE 1588-2008 time being in TAI but using the unix reference epoch.

I'm not 100% happpy with the naming of the methods however. By default IEEE 1588-2008 uses TAI with unix epoch, but the standard does not enforce this. In practice, (practically) all implementations use it however.

Fixes #378

[ChristopherRabotin]

Thanks for the PR! Could you also add a from_ptp_duration constructor, similar to https://docs.rs/hifitime/latest/hifitime/struct.Epoch.html#method.from_tai_duration.

Thanks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.87%. Comparing base (1311c4f) to head (109ee42).
Report is 52 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #379      +/-   ##
==========================================
- Coverage   84.32%   83.87%   -0.46%     
==========================================
  Files          23       24       +1     
  Lines        3720     3813      +93     
==========================================
+ Hits         3137     3198      +61     
- Misses        583      615      +32     

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[ChristopherRabotin]

Hmm, I can tackle the dependency error. It seems like the MSRV may need updating again.

[gwbres]

Minor thought,

(I also like having construction methods like these a lot, they make life much easier for the end user)
but since PTP applications are usually located around tens of nanoseconds, I would rather have from_ptp_nanoseconds instead of milliseconds ?

[georgeboot]

fair point. added

[georgeboot]

Hmm, I can tackle the dependency error. It seems like the MSRV may need updating again.

Yeah not too sure what to do about that.

[ChristopherRabotin]

Thanks @georgeboot , I'll merge this now. I'm working on fixing the lints on another branch. It'll be released with version 4.1.0 in the coming days.