Removed Debugger class

Including PHPUnit test cases in the near future.
Complete rework on ImageConverter

Collapse option parameters in `core\ImageConverter::resizeTo()` into
one single options array.
Revised Net.php to better implement the jQuery ajax pattern.

To better implement jQuery ajax pattern, moved callbacks in option from
`[ 'callbacks' => [ 'success' => function ... ] ]` into root level as
this `[ 'success' => function ... ]`.
Removed Debugger class alias.
Updated documents for new class changes.

1. Corrected scripts and service directory path, they were moved into
.private/ for a few versions.

2. Added sample code for ImageConverter and XMLConverter.

3. Added sample code for Net.

4. Added simple description for Event, EventEmitter, Deferred and
Promise.