Adds a convenience function to create a layout with a direction and a
list of constraints which are the most common parameters that would be
generally configured using the builder pattern. The constraints can be
passed in as any iterator of constraints.
```rust
let layout = Layout::new(Direction::Horizontal, [
Constraint::Percentage(50),
Constraint::Percentage(50),
]);
```
BREAKING CHANGE:
Layout::new() now takes a direction and a list of constraints instead of
no arguments. This is a breaking change because it changes the signature
of the function. Layout::new() is also no longer const because it takes
an iterator of constraints.
This allows passing an array, slice or Vec of constraints, which is more
ergonomic than requiring this to always be a slice.
The following calls now all succeed:
```rust
Table::new(rows).widths([Constraint::Length(5), Constraint::Length(5)]);
Table::new(rows).widths(&[Constraint::Length(5), Constraint::Length(5)]);
// widths could also be computed at runtime
let widths = vec![Constraint::Length(5), Constraint::Length(5)];
Table::new(rows).widths(widths.clone());
Table::new(rows).widths(&widths);
```
