Hello Carlos,
I found the reference from CMB2 plugin documentation and give it a try.
This framework is well written and simple to understand, thanks for such great efforts.
I git cloned it and changed my namespace (CP),
I uncommented the code to activate admin pages and visited to admin page and it gave me error.

call_user_func_array() expects parameter 1 to be a valid callback, class ‘CP\Admin’ not found in C:\xampp\htdocs\plugindevelopment\wp-includes\class-wp-hook.php on line 286

After changing the line in config file,
from

«function» => __NAMESPACE__.»\Admin::option_page»,
to

«function» => __NAMESPACE__.»Admin\Admin::option_page»,
 

It worked, but content in the function dosent came to screen.

again I changed function to,

$title = ‘<h2>Hello World</h2>’;
echo $title;
// return $title;

It worked.

Is this need to do or there is another way to do it.

By the way, I am very thankful for such a helpful framework.