Add generic `range` function to the prelude

[brson]

uint::range is one of the most common ways to iterate, but the uint:: prefix is a bit unsightly. Add a generic range function, parametrized over whatever traits are appropriate and add it to the prelude. Then convert all uses of range.

[brson]

Integer inference could make this strategy backfire. One most often wants to iterate over uints but range(0, 10) will infer ints. Maybe inference will pick up the correct type from the closure body but I'm not sure.

[sophiebits]

If you want uints inside the loop, it doesn't seem so strange to have to write range(0u, 10u).

[thestinger]

@brson: what would you think about a generic trait for enumerated types with a to method? So something like for 5i.to(&10) |x| { ... } or for "foo".to(&"bar") { ... }.

Here's Haskell's approach to this:

http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Enum

I think #6023 would be a reasonable approach to the integer inference issue (inferring, but not falling back to int).

[thestinger]

Implemented as an iterator by #8216.