Strict mode: Fix readme.md and fix getTIN function

[ortegafernando]

Hi, I have updated readme.md file and also fix getTIN function to return only upper version of TIN.

Before:

    public function getTIN(): string
    {
        if (null !== $string = preg_replace('#[^[:alnum:]\-+]#u', '', $this->tin)) {
            return strtoupper($string);
        }
        return '';
    }

After:

    public function getTIN(): string
    {
        return strtoupper($this->tin);
    }

Otherwise, validate function using this $tin = $this->getTIN(); at the beginning is not using the correct stricted version of TIN.

The place in where TIN is "normalized" is in your new parse function, so there is not necessary to normalized it again in getTIN funcion.

NOTE: if you want, you can even publish getTIN() as this:

    public function getTIN(): string
    {
        return $this->tin;
    }

but I think that strtoupper function doesnt hurt.

[drupol]

I would prefer to keep that in the existing normalize function. WDYT?

[ortegafernando]

I agree you

[drupol]

How about keeping the "algorithm" side of things internally and expose a simpler interface?

In this case, I would just name this method isSupported() ? WDYT ?

[ortegafernando]

Yes, this is better, I agree you, better isSupported()

[drupol]

Can you please resubmit your PR using a different branch, you should not use master but create your own branch.