Fix for issue #73

Should now correctly line break for `<br>`, `<BR>`, `<br/>`, `<BR/>`

graph.txt:
```
sequenceDiagram
  participant Alice
  participant Bob
  Alice->John: Hello John, how are you?
  loop Healthcheck
  John->John: Fight against hypochondria
  end
  Note right of John: Rational thoughts <br/>prevail...
  John-->Alice: Great!
  John->Bob: How about you?
  Bob-->John: Jolly good
```

mermaid output:
![mermaid txt](https://cloud.githubusercontent.com/assets/8934224/5586209/a59ec9b0-9093-11e4-8ddf-94c3830705a0.png) 

`phantomjs -v` outputs `1.9.8`