`<md-checkbox>` provides the same functionality as a native `<input type="checkbox">`
enhanced with Material Design styling and animations.

<!-- example(checkbox-overview) -->

### Checkbox label
The checkbox label is provided as the content to the `<md-checkbox>` element. The label can be 
positioned before or after the checkbox by setting the `labelPosition` property to `'before'` or
`'after'`.

If you don't want the label to appear next to the checkbox, you can use 
[`aria-label`](https://www.w3.org/TR/wai-aria/states_and_properties#aria-label) or 
[`aria-labelledby`](https://www.w3.org/TR/wai-aria/states_and_properties#aria-labelledby) to 
specify an appropriate label.

### Use with `@angular/forms`
`<md-checkbox>` is compatible with `@angular/forms` and supports both `FormsModule` 
and `ReactiveFormsModule`.

### Indeterminate state
`<md-checkbox>` supports an `indeterminate` state, similar to the native `<input type="checkbox">`.
While the `indeterminate` property of the checkbox is true, it will render as indeterminate 
regardless of the `checked` value. Any interaction with the checkbox by a user (i.e., clicking) will
remove the indeterminate state.

### Theming
The color of a `<md-checkbox>` can be changed by using the `color` property. By default, checkboxes
use the theme's accent color. This can be changed to `'primary'` or `'warn'`.