Code.js

function updateMenu_(menu, items) {
    var menuIterator = makeIterator_(items);
    while (true) {
        menu.addItem(menuIterator.get().name, menuIterator.get().fn);
        if (menuIterator.next().done) break;
    };
}

function getScriptFunctionsAsMenuItems_(context) {
    return Object.keys(context).filter(function (key) { return key.slice(-1) !== "_" && key !== "onOpen" && typeof this[key] === "function" }, context).map(function (item) {
        return { name: item, fn: item };
    });
}

function L() {
    Browser.msgBox("L");
}

function f1() {
    Browser.msgBox("f1");
}

Tools.js

function makeIterator_(array) {
    var nextIndex = 0;
    return {
        next: function () {
            nextIndex++;
            return nextIndex < array.length ?
                { value: array[nextIndex], done: false } :
                { done: true };
        },
        get: function () {
            return nextIndex < array.length ? array[nextIndex] : undefined;
        }
    };
}

Ui.js

function onOpen() {
    var self = this;
    var menu = SpreadsheetApp.getUi().createMenu("All script functions");
    updateMenu_(menu, getScriptFunctionsAsMenuItems_(self));
    menu.addToUi();
}