Adding async.h to the README.
Changing 2015 to 2014 in the last changelog entry.
Merge pull request #158 from jsdevel/adding-async.h-to-the-readme

Adding async.h to the README.
Merge pull request #159 from jsdevel/fixing-changelog-in-nan.h

Changing 2015 to 2014 in the last changelog entry.