Compact

[ryanpdwyer]

• Adds a to_compact method to Quantity, as discussed in Support for normalization #151.
• Adds infer_base_units, a helper method used by to_compact, to utils.
• Adds tests of to_compact

[hgrecco]

While I am definitely +1 on adding the compact method that you propose I am not happy about hardcoding the prefixes (and in 2 places). You can access all the prefixes from the registry. To get the unprefixed name we could modify get_name to have an extra parameter (strip_prefix?) or similar defaulting to the current behavior.

This is not just a aesthetic choice. Is part of Pint design philosophy to avoid hardcoded values and making everything part of the registry.

Additionally, this will also help when we try implement this compact for non SI units, but this are future plans when systems are fully implemented.

[hgrecco]

Sorry but only now this came again to my attention. It looks really good. I will merge it next week.

[hgrecco]

thanks!