Instead of putting script tags in the article for the Pym script source, enqueue!

[benlk]

https://github.com/INN/pym-shortcode/blob/8047878a94ed8740fdc6cd3feb334168d07263dc/pym-shortcode.php#L61-L68

This should instead:

1. If the pymsrc attribute is set, enqueue that script in the footer.
2. If pymsrc is not set, enqueue the default script. (See also Provide a setting to allow site admins to opt into using the CDN version of Pym #31)

[benlk]

(One concern: this means that after all the filters are applied, post_content won't have all the scripts necessary for Pym embeds.)