(RFC) replace old_iter::repeat with the Times trait

[thestinger]

I don't have a strong opinion on the function vs. method, but there's no point in having both. I'd like to make a repeat adaptor like Python/Haskell for turning a value into an infinite stream of the value, so this has to at least be renamed.

[catamorphism]

I'm not sure how I feel about this change; sometimes repeat seems to make more sense to me, other times the n.times syntax makes more sense to me. (Though as a functional programmer, I usually use the former.)

I suggested that @thestinger make this an "RFC" since it's a change the affects a lot of existing code.

[kud1ing]

See also #2143

[bstrie]

Unified function call syntax would make the "function vs method" issue moot, so I'm fine accepting this for now.