this is a very small, **non-breaking**, alteration to the signature of
`Histogram`'s constructor.

rather than accepting an `impl Iterator`, this commit changes the
parameter of `Histogram::new()` to be an `impl IntoIterator` instead.
this does not affect the existing contract because of the blanket
`impl<I: Iterator> IntoIterator for I` implementation provided by the
standard library.

by accepting `IntoIterator` however, callers providing a collection such
as a `[f64; 5]` array or a `Vec<f64>` vector do not need to invoke
`into_iter()` themselves at the call-site.

```rust
// now, constructing a histogram needn't involve `into_iter()`...
use prometheus_client::metrics::histogram::Histogram;
let histogram = Histogram::new([10.0, 100.0, 1_000.0]);
```

this leans on the same sugar used by `for {}` loops, see the relevant
section of the `std::iter` documentation here:
<https://doc.rust-lang.org/stable/std/iter/index.html#for-loops-and-intoiterator>

no changes are needed within `Histogram::new()` because we already call
`into_iter()` on the provider iterator when appending `f64::MAX` and
collecting the buckets into a `Vec<_>`.

Signed-off-by: katelyn martin <[email protected]>

this commit addresses some chores related to the package manifest, and
the changelog, noticed in review.

see:

- <prometheus#243 (comment)>
- <prometheus#243 (comment)>

Signed-off-by: katelyn martin <[email protected]>