now key is utf8encoded in bind function, functions sign, verifySignature  works with base64 url safe encoded Strings instead of previous List<int>. Tests are updated in the same manner.
small fix, proper versioning 0.3.0
Merge pull request #17 from cleandart/backendSignStrings

now key is utf8encoded in bind function, functions sign, verifySignature... v0.3.0