Add methods to use a `Timecode` struct as a template about timecodekit

[orchetect]

Upon further reflection, the most common use case would likely be setting new time component values while retaining rate, limit, base and format.

In that case, each current initializer could receive an overload that takes a Timecode instance as a template.

let tcTemplate = Timecode(
    at: ._29_97,
    limit: ._100days
    base: ._80SubFrames
    format: [.showsSubFrames]
)

let tc2 = try Timecode("01:20:15:10", template: tcTemplate)
// tc2.frameRate == ._29_97
// tc2.limit == ._100days
// tc2.subFramesBase == ._80SubFrames
// tc2.stringFormat == [.showsSubFrames]

[orchetect]

This is addressed in the forthcoming 2.0.0 release.

A new Timecode.Properties struct that contains frameRate, limit, and base can be passed to Timecode initializers and various other methods.