Follows this link on mousedown instead of click.
This will save precious milliseconds that otherwise spent
on waiting for the user to release the mouse button. Since an
AJAX request will be triggered right way, the interaction will
appear faster.
Note that using [up-instant] will prevent a user from canceling a
click by moving the mouse away from the link. However, for
navigation actions this isn't needed. E.g. popular operation
systems switch tabs on mousedown instead of click.
Example
<a href="/users" up-follow up-instant>User list</a>
Accessibility
If the user activates an element using their keyboard, the up:click event will be emitted
on click, even if the element has an [up-instant] attribute.
