added persistence to entity API (read and write)

docs/scarpet/api/Entities.md

@@ -128,6 +128,10 @@ query(e,'type')  => villager
 Returns a valid string to be used in commands to address an entity. Its UUID for all entities except
 player, where its their name.
 
+## `query(e, 'persistence')`
+
+Returns if a mob has a persistence tag or not. Returns `null` for non-mob entities.
+
 <pre>
 run('/kill ' + e~'command_name');
 </pre>
@@ -411,9 +415,15 @@ Sets the corresponding component of the motion vector.
 
 Adds a vector to the motion vector. Most realistic way to apply a force to an entity.
 
-### `modify(e, 'custom_name'), modify(e, 'custom_name', name)`
+### `modify(e, 'custom_name')`, `modify(e, 'custom_name', name)`, `modify(e, 'custom_name', name, visible)`
 
-Sets the custom name of the entity.
+Sets the custom name of the entity. Without arguments - clears current custom name. Optional visible affects
+if the custom name is always visible, even through blocks.
+
+### `modify(e, 'persistence', bool?)`
+
+Sets the entity persistence tag to `true` (default) or `false`. Only affects mobs. Persistent mobs
+don't despawn and don't count towards the mobcap.
 
 ### `modify(e, 'age', number)`