add internal blpapi session wrapper

This provides an abstraction for the web server for the blpapi-node API.
introduce user-defined configuration

This change introduces configuration via .json files, environment
variables, and command-line parameters.  Defaults are baked into the
config.js' module.
introduce index.js

Implement the BLPAPI web proxy. Only historical request/response is
supported for now.
add examples/ directory

Simple API examples:
- ex1.sh
    Shell script performing two historical data requests
- HistoricalDataRequest.js
    NodeJS client example
- cfg.json
    Example configuration file for the proxy
- jqtest.html
    Browser example using JQuery and JSONP