Implement endroid/qr-code support

[SavageCore]

I have left out readme changes as it needs updating further, default provider still listed as ImageChartsQRCodeProvider for example.

Usage

$qrProvider = new RobThree\Auth\Providers\Qr\EndroidQrCodeProvider('ffffff', '0000000', 0, 'H');
$tfa = new RobThree\Auth\TwoFactorAuth('My Company', 6, 30, 'sha1', $qrProvider);

[RobThree]

I am really not very much familiar with the whole composer thing; shouldn't this require a reference in the composer.json file as it's a dependency?

[MasterOdin]

Anything that can be helped with to see this merged and incorporated into a new release? Similar to the suggestion in #39, composer.json can be modified to use the suggest block to propose dependencies that will enhance the package, but are not strictly necessary:

"suggest": {
  "endroid/qr-code": "Needed for EndroidQrCodeProvider"
}

Then optionally install it to require-dev to be used for writing a test case with it.

[RobThree]

I have merged this one, as wel as #39. If someone would like to update the README and make a PR that would be appreciated!

[MasterOdin]

sure, I can do that.

[willpower232]

thanks @MasterOdin