(chore) Use a dummy module to re-export Assoc.

Thanks to @aochagavia for bringing this up.
Merge pull request #181 from reem/feat/export-assoc

(chore) Use a dummy module to re-export Assoc.
(fix) Call the main handlers catch method.

Right now errors in the main handler are immediately assumed
to be unhandleable. This changes the behavior of Iron to call
the catch method.

The interaction with chain's catch method is unresolved.
(chore) Remove the explicit dependency on http in the hello-world example.
Merge pull request #184 from reem/fix/handler-catch-no-middleware

(fix) Call the main handlers catch method.
Merge pull request #185 from reem/cleanup/remove-http-example

(chore) Remove the explicit dependency on http in the hello-world example.