Enabling single parameter in enyo.asyncMethod
Update CHANGELOG.md
Add test cases for enyo.asyncMethod

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #643 from enyojs/LEX-ASYNCMETHOD

Enabling single parameter in enyo.asyncMethod

Reviewed-By: Ben Combee (ben.combee@lge.com)