Support for parsing W3C date format level 6 (with fraction of seconds)

```
Date.parse() doesn't seem to be able to parse the 6th level of the W3C date
format [1]:

Complete date plus hours, minutes, seconds and a decimal fraction of a
second
YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)

I'm willing to add support for this, but I didn't found how to build datejs ?

[1] http://www.w3.org/TR/NOTE-datetime
```

Original issue reported on code.google.com by `arnaud.lb` on 16 Jan 2012 at 12:58