PHP 8 and psr-4 autoloading support

[faizanakram99]

No description provided.

[subiabre]

@Sybio have you had time to review this MR? It fixes #24 and updates the library to PSR which is highly important for this package and the developers who trust it.

I've reviewed it and it looks good to me, if that is of any help. I'm mainly tagging you because I see this pull request has no reviewers assigned so maybe you had not seen it yet.

[gesior]

There is only one thing missing. In PHP 8.0 images are no longed resources. They are GdImage objects.
I had to change:

if (is_resource($frames[$i])) { // Resource var

to:

if ($frames[$i] instanceof GdImage || is_resource($frames[$i])) { // Resource var

to make it load array of generated images.

[faizanakram99]

@gesior

Thanks, changed