support for filesystem in simulator

sim/state/filesystem.ts

@@ -0,0 +1,18 @@
+namespace pxsim.files {
+    export function appendLine(filename: string, text: string) {
+        const b = board();
+        b.fileSystem.append(filename, text + "\r\n");
+    }
+    export function appendString(filename: string, text: string) {
+        const b = board();
+        b.fileSystem.append(filename, text);
+    }
+    export function appendNumber(filename: string, value: number) {
+        const b = board();
+        b.fileSystem.append(filename, value.toString());
+    }
+    export function remove(filename: string) {
+        const b = board();
+        b.fileSystem.remove(filename);
+    }
+}