Change main API

Completely change the way you use the Opbeat client
Rename dsn to api
Make the client.process method private
Remove .version function
Allow the severity level of exceptions to be set in options
Rename options.handleExceptions to options.captureExceptions
Cleanup tests
Ensure that handleUncaughtExceptions can be called multiple times
We don't log stuff to Opbeat, we sent it
Move the main client code to the index file