The flag FILTER_SANITIZE_STRING is deprecated in PHP 8.1.0

[domeales-paloit]

Hi there,

We love Gitium, nice one!

We have just noticed after upgrading PHP that the flag FILTER_SANITIZE_STRING is deprecated in PHP 8.1.0.

I would like to submit a PR to replace the use of FILTER_SANITIZE_STRING with FILTER_SANITIZE_FULL_SPECIAL_CHARS. Based on the PHP docs for FILTER_SANITIZE_STRING it says:

Deprecated as of PHP 8.1.0, use htmlspecialchars() instead.

and for FILTER_SANITIZE_FULL_SPECIAL_CHARS it also says:

Equivalent to calling htmlspecialchars() with ENT_QUOTES set.

Therefore, it looks like FILTER_SANITIZE_FULL_SPECIAL_CHARS is a suitable replacement for FILTER_SANITIZE_STRING.

To note also, the constant FILTER_SANITIZE_FULL_SPECIAL_CHARS is available in PHP versions >= 5.3.3.

Would you be happy to receive this PR?