A macro for merging vectors.
```rust use vecmerge::vecmerge;
fn main() { assert_eq!(vec![1,2,3,4,5,6], vecmerge!([1,2,3] + [4,5] + [6]));
let a = vec![1,2,3];
let b = vec![6];
assert_eq!(vec![1,2,3,4,5,6], vecmerge!(a + [4,5] + b));
assert_eq!(vec![1,2,3,4,5,6], vecmerge!(vec![1,2,3] + vec![4,5,6]));
} ```