First release candidate

Recent changes include:

• Dict\flatten added, which takes a traversable of keyedtraversables for consistency with {Vec,Keyset}\flatten
• Keyset\from_async added for consistency with {Dict,Vec}\from_async
• Keyset\merge, Dict\merge, and Keyset\union now require at least one argument (all are variadic)
• C\{min,max_by,min,min_by} have all been removed in favor of their replacements in the Math\ namespace
• Math\min and Math\max now take traversables instead of variadics
• Math\minv and Math\maxv have been added as variadic alternatives

This addresses all known inconsistencies in the HSL, so we expect this to be the final release of the HSL before v1.0.