Add support for new ES6 numeric literals

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-literals-numeric-literals

```
BinaryIntegerLiteral ::
  0b BinaryDigits
  0B BinaryDigits

BinaryDigits ::
  BinaryDigit
  BinaryDigits BinaryDigit

BinaryDigit :: one of
  0 1

OctalIntegerLiteral ::
  0o OctalDigits
  0O OctalDigits

OctalDigits ::
  OctalDigit
  OctalDigits OctalDigit

OctalDigit :: one of
  0 1 2 3 4 5 6 7
```