Add library with namespaces

A composer package exists: https://packagist.org/packages/faisalman...-excel-php

See this old thread https://ellislab.com/forums/viewthread/246558/ - This is an example about how to activate Composer in CodeIgniter (a config setting is to be touched) and how to install a package.

Have a look at Composer's documentation too: https://getcomposer.org/doc/

After installing the package faisalman/simple-excel-php try its sample usage code (that is on the github page) within a controller to test whether it works.