HashMap Macro

Creates a HashMap from provided key/value pairs.

Usage

```rust use std::collections::HashMap; use hashmap_macro::hashmap;

let m: HashMap<&str, u32> = hashmap![]; let m: HashMap<&str, u32> = hashmap!("a" => 1); let m: HashMap<&str, u32> = hashmap! { "a" => 1, "b" => 2, }; ```

Inspired by Jon Gjengset's Crust of Rust: Declarative Macros