Add binary integer literals

_This issue was originally filed by [ladicek@gmail.com](https://github.com/search?q=ladicek%40gmail.com&type=Users)_

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When working with bits and bytes, having binary integer literals comes handy, as a lot of languages acknowledged (Python, Ruby, Java, even GCC has them as an extension). I believe that the reasoning behind adding binary literals to Java 7, as per http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000929.html, is equally valid to Dart, and therefore I propose to add binary literals in the same form ("0b100000" as an equivalent of "0x20"). I think that implementation is no concern (I did it in the VM and it was pretty straightforward, as I describe in http://ladicek.github.com/2012/04/29/hacking-the-vm-adding-binary-integer-literals.html).