phar API update

Hi,

I've just implemented these features:

1. new getContents() method allows directly retrieving file contents.
   Here is a full-circle example:
   <?php
   $phar = new Phar('blah.phar');
   $phar['a.txt'] = 'hi';
   echo $phar['a.txt']->getContents();
   ?>

2. addFile/addEmptyDir/addFromString. API is identical to ext/zip
   <?php
   $phar = new Phar('blah.phar');
   $phar->addEmptyDir('hello');
   var_dump($phar['hello']->isDir());
   $phar->addFile('/path/to/file.txt');
   var_dump($phar['/path/to/file.txt']->getContents());
   $phar->addFile('/path/to/file.txt', 'file.txt');
   var_dump($phar['file.txt']->getContents());
   $phar->addFromString('localname.txt', 'hi');
   var_dump($phar['localname.txt']);
   ?>

Still left to do:

1. fix up conversion/compression and decide how best to do this
2. buildFromDirectory (Steph)

Not going to do:

1. $phar['access']['directory']['this']['way']

Greg