Auto merge of #23347 - aturon:stab-misc, r=alexcrichton

This commit deprecates the `count`, `range` and `range_step` functions
in `iter`, in favor of range notation. To recover all existing
functionality, a new `step_by` adapter is provided directly on `ops::Range`
and `ops::RangeFrom`.

[breaking-change]

r? @alexcrichton

src/libstd/sys/unix/os.rs

@@ -286,7 +286,7 @@ pub fn args() -> Args {
     let vec = unsafe {
         let (argc, argv) = (*_NSGetArgc() as isize,
                             *_NSGetArgv() as *const *const c_char);
-        range(0, argc as isize).map(|i| {
+        (0.. argc as isize).map(|i| {
             let bytes = CStr::from_ptr(*argv.offset(i)).to_bytes().to_vec();
             OsStringExt::from_vec(bytes)
         }).collect::<Vec<_>>()