Insert custom attributes on the element

[maciejfikus]

Hi Odan,
first of all, thanks for all your work on this package. It does the job :-)

I am currently working on a project with very high focus on the performance. I need to be able to defer loading of uncritical CSS (https://web.dev/defer-non-critical-css/).

In essence, my desired assets function output should look similar to:

<link rel="preload" href="../css/components/style.css" as="style" onload="this.onload=null;this.rel='stylesheet'">

In order to do so, I've added a possibility to add custom attributes to the final html element. What is important, it is capable to override default attributes specified in the engine.

Default behavior is unchanged, so it is fully compatible with current implementations.

I've also included tests and readme update.

Example usage:

{{ assets({files: [
    '@assets/css/components/one.css',
    '@assets/css/components/two.css'
], attributes: {
    rel: 'preload',
    as: 'style',
    onload: 'this.onload=null;this.rel=\'stylesheet\''
}, name: 'test'}) }}

Output:

<link rel="preload" type="text/css" href="cache/test.d9dd34444345f823e0a667677cbb5864e9840e0b.css" media="all" as="style" onload="this.onload=null;this.rel='stylesheet'" />

Same thing is possible with .js files for any reason.

Cheers!

[odan]

Hi @maciejfikus Thanks for the PR. This looks very good. Give me some time to check it.