Allow bitmap values to take up multiple bits (more than true/false)

In addition to the original usage (fully backwards compatible), you can now do:
```javascript
PREFERENCES_BITMAP_KEYS = [
// ['NAME', NUMBER_OF_BITS, [OPTIONS, ...] ],
  ['PREF1', 1, [false, true]],
  ['PREF2', 5, ["0", "1", "2"]],
  ['PREF3', 1, ["0", "1"]]
];
tf = new AutoBits({
    map: PREFERENCES_BITMAP_KEYS,
    debug: true
});
tf.setPreference('PREF1', true);
tf.setPreference('PREF2', '2');
tf.getPreference('PREF1');  // true
tf.getPreference('PREF2');  // '2'
```