Measure of length

[JonasBarka]

Fixes #526

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• Implementation is clean
• Code adheres to the existing coding standards; e.g. no curlies for one-line blocks, no redundant empty lines between methods or code blocks, spaces rather than tabs, etc.
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Note the interaction between parameters decimals and minPrefix as described in the comment to one of the unit tests.

Only maxPrefix and minPrefix are new options, but I added all options to the readme description of ToMetric.

[dnfclas]

All CLA requirements met.

[clairernovotny]

The copyrights at the top of the file, if any, should be simply Copyright (c) .NET Foundation and Contributors

Alternatively, it can be removed as it's in the project root.

[clairernovotny]

Same as above

[SimonCropp]

@JonasBarka do you still want this one merged? if so can you address the comments and rebase