added Angular Directives Book by Alex Vanston
Merge pull request #59 from dadepo/angular-directives-book

added Angular Directives Book by Alex Vanston. Thanks @dadepo, I should have thought of adding this one, seeing that I was one of the technical reviewers. Doh!
Merge pull request #2 from jmcunningham/master

added Angular Directives Book by Alex Vanston