add autoload alia function

Signed-off-by: Louis <hotmailgotohell@gmail.com>

### What's new

This patch helps developers use library alias in autoload.

### How to do

To use alias in autoload, simply add a " as * " in the autoload config item.

<code>$autoload['libraries'] = array('my_lib1','my_lib2 as my2');</code>

as you can see in the case, it's totally downward compatibility.