Allow content to be padded

Sometimes it can useful to pad content out to a particular length (requested in issue #14)
```php
$padding = $climate->padding(50);
$padding->pad("Line one stuff");
$padding->pad("More stuff on line two");
$padding->pad("Final content on line three");
```
Will output:
```
Line one stuff....................................
More stuff on line two............................
Final content on line three.......................
```

If no width is passed to the padding method then the full terminal width is used.
The length can also be specified using the length() method.

An alternative character can be specified with the padWidth() method, or as the second parameter to padding().
Multiple characters can also be used
```php
$padding = $climate->padding(5, ".-");
$padding->pad("AAA");
$padding->pad("BB");
$padding->pad("CCCC");
```
Will output:
```
AAA-.-
BB.-.-
CCCC.-
```

Would you like me to submit a pull request for the documentation to explain all the features?