v2.0.0.

Backward incompatible changes in 2.0:

1. Required browsers' config now wants a natural-language entries with
   semver-compliant version names, instead of objects with properties browserName,
   majorVersion etc. In other words:

   Old config that is no longer accepted:

   browsers:
       - browserName: 'Firefox'
         majorVersion: 30
       - browserName: 'IE'
         majorVersion: 9
         os: 'Windows 7'
   

   New config (nicer and more powerful)

   browsers:
       - 'Firefox >=30'
       - 'IE 9 on Windows 7'
   

2. The command line option --browser that runs a browser executable to run the
   tests has been renamed to --run-browser

3. Attester 2.0 is tested on NodeJS 0.10. Attester 1.x used to be tested on NodeJS 0.8.

   In practice, both Attester 1.6 and 2.0 should run fine either on Node 0.8 or 0.10,
   but we will no longer support Node 0.8 for new releases.