infer scale of a grade

[musoke]

A lot of grades' scales are unambiguous. For example

• V2 is always V-scale
• 5.7 is always YDS
• HVS is always British adjectival

Others are not

• 7a could be French sport or British technical or Brazilian (or Font if capitalization is not trusted)
• Finnish, Norwegian, Ewbank, South African Ewbank

Some can be distinguished if the discipline is known:

• on boulder problem, 7a is Font with non-standard capitalization. On a sport route it's ambiguous.

This could be implemented by attempting to parse as all known grades and checking if exactly one parse succeeds.