Convenience methods

Jacques,

I added some convenience methods that may make your users' code look a little cleaner - and did some small cleanup items.

To summarize, what used to look like this:

```

$curl = new Curl;
$curl->changeToPost();
$curl->setAddress('http://www.example.com/');
$curl->setPostValue(array(
    'foo' => 'bar',
));
$curl->makeRequest();

```

might now look like this:

```

$curl = new Curl;
$curl->post('http://www.example.com', array(
    'foo' => 'bar'
));

```

The same goes for ``` Curl::get ```, ``` Curl::put ```, and ``` Curl::delete ```.

They're yours if you want them; if not, that's cool too.