Add prefix api/v1 to all API endpoints

Add urgent to notifications

Add custom metrics

Add scheduled notifications

Add imageUrl, requireInteraction, customData and starred

Merge action buttons

Merge pull request pushpad#2 from 125m125/patch-2

Support UTF-8 characters in notifications

Merge pull request pushpad#1 from 125m125/patch-1

Use hex-encoding for HMAC-SHA1 signature

Prevent broadcasting when you pass null to deliverTo

Add "id" to readme