Add gitignore that ignores rbx temp files
Fix BCryptHash type to dump to a string

* Most database drivers would have stringified the BCyrpt::Password
  instance, however some alternate DBs may not always do it
  properly. This change ensures that the correct type is always
  dumped.
Change bcrypt type to dump a utf-8 string if possible

* This is required by the yaml adapter to properly serialize the
  string into something that can be serialized as a string
  primitive and not a binary string, which is not supported by
  safe_yaml at the moment.
Update travis config to disable tests for rbx in 1.8 mode