Created a tab() method

This is useful when using a background colour, but only wanting the text to have the background
```php
$climate->backgroundRed("\tContent");
```
The above would colour the whitespace before "Content" in red (not desirable).

The only option to avoid this would be
```php
$climate->inline("\t")->backgroundRed("Content");
```

However the following is much more expressive, and avoids ugly escape characters
```php
$climate->tab()->backgroundRed("Content");
```

The class extends the Br class to support a variable number of tabs, eg:
```php
$climate->tab(3)->out("Tabbed in really far");
```