Make Slim PSR compliant

## PSR Compliance

These updates change the <code>Slim/Log</code> class to make it PSR-3 compliant as-well as general tweaks on some other files to make them PSR-2 compliant.

I left support for some old methods in <code>Slim/Log</code> to keep it backwards compatible, but I have marked them with <code>DEPRECATED</code> so they can be removed in the future.

## Slim / Log methods
The new class provides access to the following methods:
```php
 $log->debug( mixed $object, array $context = array() );
 $log->info( mixed $object, array $context = array() );
 $log->notice( mixed $object, array $context = array() );
 $log->warning( mixed $object, array $context = array() );
 $log->error( mixed $object, array $context = array() );
 $log->critical( mixed $object, array $context = array() );
 $log->alert( mixed $object, array $context = array() );
 $log->emergency( mixed $object, array $context = array() );
 $log->log( mixed $level, mixed $object, array $context = array() );
```
As per the PSR-3 standard, the following functions are marked as <code>DEPRECATED</code> but still work, as they are being mapped to the new methods:
```php
 $log->warn( mixed $object, array $context = array() );
 $log->fatal( mixed $object, array $context = array() );
 $log->write( mixed $object, int $level);
```

## Placeholders in error messages
As per the PSR-3 standard, messages can contain placeholders in the format <code>{placeholder_name}</code>. No spaces may be used between the placeholder's name and brackets. The optional context array needs to contain the value for each placeholder in-order for it to be replaced.

Here is an example:
```php
 $log->debug( 
     "{greeting} {place}",
     array(
         "greeting" => "Hello"
     )
 );
```

Will send the message <code>"Hello {place}"</code> to the log writer.