[PR][web-php][#53][master] - Add json_encode()ded endpoint to PHP releases list + content type adjustments

You can view the Pull Request on github: https://github.com/php/web-php/pull/53 Warning: according to github, the Pull Request cannot be merged without manual conflict resolution! Pull Request Description: We usually warn PHP users to avoid unserialize remote or untrusted data but at the same time php.net only offers a serialized endpoint for PHP releases. This commit: - adds a JSON endpoint that can be an option to avoid the serialized endpoint - sets a proper Content-Type response header for both serialized - text/plain - and json - application/json - endpoints - simplifies URLs exchanging &serialize=1 and &json=1 for &serialize and &json respectively Cheers!