Add function for handling date strings in IE8

IE8 doesn't handle `new Date("YYYY-mm-dd")` properly, so I've added a function `parseDate` which works in IE8. Screenshot of functioning dateinput test app below:
![screenshot from 2014-02-24 15 21 58](https://f.cloud.github.com/assets/86978/2251224/ed3041ca-9d99-11e3-91de-b9fc2e153f9b.png)