Implement FromStr for data types

[TehPers]

Implements FromStr for Date, DateTime, Duration, and Time by delegating to each type's respective parse_str method.

Date and DateTime also have parse_str_rfc3339 (parse_str accepts a Unix timestamp as well). This PR uses the more permissive of the two to accommodate for more input formats. Users of the library can still explicitly call parse_str_rfc3339 directly themselves for more strict parsing.

Closes #48

[codecov]

Codecov Report

Merging #49 (f3c692b) into main (4ea725c) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
+ Coverage   99.11%   99.12%   +0.01%     
==========================================
  Files           6        6              
  Lines         902      918      +16     
==========================================
+ Hits          894      910      +16     
  Misses          8        8              

Files	Coverage Δ
src/date.rs	100.00% <100.00%> (ø)
src/datetime.rs	100.00% <100.00%> (ø)
src/duration.rs	100.00% <100.00%> (ø)
src/time.rs	97.81% <100.00%> (+0.02%)	⬆️

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[samuelcolvin]

Great if you could add tests, just one or two would be great.

[TehPers]

I hooked tests into param_tests since all the types implement FromStr now and have parse_str methods. Future types could opt out of this functionality in the macro (or current types could opt-in).

[davidhewitt]

It looks to me like the tests are added and passing, so I will assume this is now fine to merge.