[pre-rfc] bind binary_search to traits instead of slice

[stebalien]

IIRC, the main thing holding stuff like this back are generalized collection traits and the main reason we don't have those is the lack of HKT.

See the following for a relevent discussion (it doesn't explicitly mention binary search but that would probably be added to the SortedSet trait):

Collection Traits, Take 2

Before we finalize everything forever, I figured we should quickly reflect on what we want to collection traits to look like. So here’s a quick sketch of the minimal API I think we should provide. Some notable points: Everything is associated types; nothing should plausibly be a collection of more than one type at once. Very little inherits from anything else. This might be unergonomic (wrangling that foo is a Stack and Seq with the same Elem type). Not sure if we should mandate that e.g. all …