Split grammar (#15)

* Move grammar parsers to entity classes

* Fix includes

* Fix Entity5 test

* Small detail

* Fix unknown keys entities

* Persistent grammar objects

* Fix grammar

* Grammar from variable

js/serialization/Serializable.js

@@ -0,0 +1,15 @@
+import Parsimmon from "parsimmon"
+
+const P = Parsimmon
+
+export default class Serializable {
+
+    static grammar = this.createGrammar()
+
+    /** @protected */
+    static createGrammar() {
+        return /** @type {Parsimmon.Parser<Serializable>} */(P.fail(
+            "Unimplemented createGrammar() method in " + this.name)
+        )
+    }
+}