function getKey() does not work with bitmasks with "holes"

[Tsaukpaetra]

I was wondering why the getKey function didn't properly return flags when I realized it apparently expects every single value to be represented in the range of bits in the mask (in addition to a "zero" dummy value at the end of it all).

For instance, a bitmask that defines values of 1, 4, 128, you won't ever get a proper array for anything but the 1 value.

I propose that since each value is supposed to represent a single-bit mask in the bitmask anyways, the function could be thus:

    public function getKey()
    {
        $value = $this->value;
        $f     = array_filter(static::toArray(), function ($key) use (&$value) {
            return  $value & $key;
        });
        return array_keys($f);
    }

[c-harris]

@Tsaukpaetra Sorry about the delay i am addressing this now.

[c-harris]

@Tsaukpaetra i have added your changes and put them into a patch version. 0.1.3