Simplify preset usage

[mrleblanc101]

Vue support arguments and modifiers.
I think this syntax would be cleaner for presets.
From:
v-motion-slide-visible-once-bottom
to:
v-motion:slide-visible-bottom.once

1. The directive name should be v-motion.
2. The animation name should be it's argument.
3. Move once to the end as a modifier.
4. Maybe accept a boolean value to enable/disable the directive conditionnaly (See :duration="0" doesn't work #263).
   v-motion:slide-visible-bottom.once="index > 3"

[mrleblanc101]

This could even allow dynamic preset usage like so:
<div v-example:[arg]="value"></div>