Dart 0.4.1 compatibility

There were some breaking API changes in the Dart 0.4.1 release that prevent this module from working in Dart latest. Namely `charCodeAt` and `charCodes` have been renamed to `codeUnitAt` and `codeUnits` respectively.

This PR includes a miner version bump in the pubspec.yaml so once you merge the changes to master all you have to do is run `pub publish` and the world will be a happier CRC32 place again.

Thanks in advance
- Joseph Moniz