NodeJS binary field issues

There's at least 3 problems in NodeJS binary field.

1. API are inconsistent across binary/comact/JSON protocols
2. compact/JSON wire format is imcompatible with other languages
   (JSON : THRIFT-3200)
3. size of compact wire format is 2x of the original binary

I propose following changes to fix this

1. Change JSON protocol return value from string to Buffer (same as binary/compact)
2. Change JSON protocol wire format to Base64 (same as other languages)
3. Change compact protocol wire format to plain binary (same as other languages)