add getters for status and validation_result

[Ricael]

After doing the conversion from HTML to AMP:

$amp_html = $amp->convertToAmpHtml();

You can check if the validation is correct or not with a single line:

$amp->getValidationResult()->getStatus();

Here is an example:

if($amp->getValidationResult()->getStatus() != ValidationResultStatus::PASS){
    print_r("ERROR\n");
} else {
    print_r("OK\n");
}