split backend into a file for each contained aspect

src/main/jastadd/backend/API.jadd

+aspect BackendAPI {
+  public void Relation.generateAPI(StringBuilder sb) {
+    sb.append(ind(1) + "// " + prettyPrint() + "\n");
+    getDirection().generateAPI(sb);
+    sb.append("\n");
+  }
+  public abstract void Direction.generateAPI(StringBuilder sb);
+
+
+  inh Relation Direction.relation();
+  eq Relation.getChild().relation() = this;
+  eq Program.getChild().relation() = null;
+
+  public String RelationComponent.nameCapitalized() {
+    return name().substring(0,1).toUpperCase() + name().substring(1);
+  }
+}