sammyjs: Resolve syntax issue with route overloads

Resolve issue with route overloads by removing the route overload that
returns void in favour of those that return Application (this matches
the library code)
Add line to README.md for added docCookies types
Merge pull request #897 from jonegerton/sammyjs

sammyjs: Resolve syntax issue with route overloads, Add line to README for docCookies