fixes #308: implement no-unused-expressions rule; ref. jshint rule W030
Merge branch 'master' of github.com:nzakas/eslint into no-unused-expressions

Conflicts:
	conf/eslint.json
no-unused-expressions rule: add test and doc mention for `a && b()`
Merge pull request #327 from michaelficarra/no-unused-expressions

fixes #308: implement no-unused-expressions rule; ref. jshint rule W030