Handle an Elli #req{} by converting it to an lmug #request{}
(lmug-elli-adptr:convert-request/1), calling the specified handler
(lmug-elli-adptr:call-handler/1) and then converting the
lmug #response{} to an Elli response tuple.

Handle request events, like request_complete, request_throw,
client_timeout, etc. Included for elli_handler conformance.
Return 'ok, irrespective of input.

Given an lmug handler and a list of Elli opts, run an lmug-elli
app and return a singleton list containing the resulting (unlinked) pid of the
underlying elli process.