Allow for tags at the end of an event with square brackets, e.g. [job]

This simple modification will allow for optional tags by adding it at the end of your event, like so:
```md
@USERNAME' life
===============

- 24/02/1955 Born
- ~1968 Summer job [job]
- 03/1976 Built a computer
- 01/04/1976 Started a company
- 04/1976-2011 Whole bunch of interesting events [something]
```

These can then be easily styled with a custom css:
```css
#life .event .time.job {
    border: 4px solid #3498db;
}
```

To see this working, I have it running myself currently and works like a charm:
http://timeline.owens.nl/