[Issue249] Support for ArrayBuffer in Filer.Buffer

1. Added proxy Buffer constructor for Filer.Buffer.
2. Added tests for new Filer.Buffer.
[issue249] forgot the glue

Need to expose FilerBuffer in place of Buffer on Filer namespace.
[issue249] fixed Buffer prototype & tests
Update README.md
Merge pull request #252 from secretrobotron/issue249

[Issue249] Support for ArrayBuffer in Filer.Buffer r=ack