Add Phync_Logger_FileDiffLogger

Added the observer to leave the log file diff.
Along with that,
- created an abstract class to put together a common process with the NamedTextLogger.
- added a test of Logger.

Example of log entry with the Phync_Logger_FileDiffLogger.

```
$ phync sample.php phynctest/
```

```
2014-02-03 23:35:43 [DIFF]
/Users/Ack/Develop/sample.php
13,15c13,15
< if (function_exists('apc_clear_cache')) {
<     if (version_compare(phpversion('apc'), '4.0.0') < 0) {
<         apc_clear_cache('user');
---
> if (!function_exists('apc_clear_cache')) {
>     if (version_compare(phpversion('apc'), '5.0.0') < 0) {
>         apc_clear_cache('users');

/Users/Ack/Develop/phynctest/application.php
38,40d37
<         // for backward-compatible (new command "install")
<         $this->registerCommand( 'bundle' , 'Onion\Command\InstallCommand' );
<         $this->registerCommand( 'self-update' );

/Users/Ack/Develop/phynctest/sample.link is link.
/Users/Ack/Develop/phynctest/ticket01.gif is binary.
```