Add prefix methods for Week and Quarter Types.

[Ianlmgoddard]

partially tackles #163

I haven't included prefixes for Microsecond or Nanosecond because as far as I can tell, DateTimes are only defined up to millisecond precision (see JuliaLang/julia#31525). I wasn't sure if we wanted to display DateTime Intervals with greater precision than what is available for DateTimes.

I also haven't added tests for Quarter because it's not clear to me how to get around the fact that this type was only introduced in Julia v1.6. Any advice there would be appreciated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.25%. Comparing base (f873f70) to head (abdb3f8).
⚠️ Report is 77 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
+ Coverage   81.09%   81.25%   +0.15%     
==========================================
  Files          11       11              
  Lines         603      608       +5     
==========================================
+ Hits          489      494       +5     
  Misses        114      114              

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[omus]

I also haven't added tests for Quarter because it's not clear to me how to get around the fact that this type was only introduced in Julia v1.6. Any advice there would be appreciated.

Use conditional blocks like:

if VERSION >= v"1.6"
    ...
end

Which allows you to only run code if the Julia version is above or equal to 1.6.0.

It shouldn't matter here but if you use @static before the if Julia can do the check at compile time allowing you to write unsupported syntax.

[LilithHafner]

Thanks for fixing these missing prefixes!

[LilithHafner]

Suggested change

	# `Quarter` defined after Julia1.6.
	# `Quarter` defined in Julia v1.6.

[LilithHafner]

If we'd like it to "just work" instead of throwing,

Suggested change

	# informative error if no prefix is defined for the given type.
	prefix(T::Type{<:Period}) = error("A prefix for period $T has not yet been defined")
	# Full name if no prefix is defined.
	prefix(T::Type{<:Period}) = string(T)