Accept items by iterator instead of slice

[jacobtread]

Description

Replaces the handling for adding multiple items to the Select, FuzzySelect, MultiSelect, and Sort they currently take a slice containing any number of values that can be converted into String through ToString, this change replaces taking a slice with instead taking anything that implement IntoIterator where the item is ToString.

This allows the items function to take any collection of values rather than only allowing slices, thus making something like the following possible:

struct MyItem {
  name: String,
  // .. other struct items
}

let collection: Vec<MyItem> = vec![  /* Some list of items */ ];
let item_names = collection
  .iter()
  .map(|item| item.name.as_str());

Select::new()
  .items(item_names);

Changes

• Make items, items_checked (and similar functions) accept an iterator instead of a slice
• Add tests for the new iterator items function

[Gordon01]

I believe #223 may now be closed