Add append() method to MicropythonFsHex

[microbit-carlos]

microbit-fs/src/micropython-fs-hex.ts

Lines 81 to 90 in a418ade

	append(filename: string, content: string): void {
	if (!filename) {
	throw new Error('Invalid filename.');
	}
	if (!this.exists(filename)) {
	throw new Error(`File "${filename}" does not exist.`);
	}
	// TODO: Implement this.
	throw new Error('Append operation not yet implemented.');
	}