Version 0.15.2

Feature requests and some bug fixes:

• allow a callback to be passed into the client.sendPendingData method
• consistency with .Net SDK's use of environment variables in Azure
• add getClient() method to the main module (allows for use of multiple instrumentation keys)
• add support for specifying port number in the endpoint url
• drop .d.ts .js.map and definitelytyped declarations from the package