Add tests and GitHub actions

[duboism]

This PR modifies the test scripts so they can be run on modern installation. Also it set up github actions.

Technical details

• We only test PHP 5.6 to 7.4 because the code is not compatible with PHP 8.
• We need to install MicroSoft's Verdana font (for test using text). This is legal (see https://corefonts.sourceforge.net/).
• Postscript output is not tested because I have issues with the Helvetica font. I think it's doable.
• PDF output is not tested because it requires the old PDFlib extension so there is 0 chances this works (it should be redone in another PR).

[duboism]

Any news ?

[ashnazg]

Won't let this stop a merge now, but I'd prefer a more flexible approach here that doesn't force a composer installation before someone could run the testsuite. Just a simple existence check on the vendor autoload in order to require it, and fall back to the old PEAR-style require otherwise.

[duboism]

Good remark but I'm not sure I understand all the details of it. Just testing the existence of vendor/autoload.php would be enough ? Do you know a package that does that (so I can take inspiration from it) ?

[ashnazg]

if (file_exists('vendor/autoload.php')) {
    // use composer if available
    require_once 'vendor/autoload.php';
} else {
    // otherwise rely on classic PEAR include_path
    require_once 'Image/Canvas.php';
}

[duboism]

Thanks @ashnazg for merging this.

[Neustradamus]

Thanks to @duboism for this PR and @ashnazg for merging!
Good job!

Can you add "Issues" section?