Add option to run CouchDB with Erlang's profiling tools

Erlang comes with a set of code coverage and profiling tools that can be helpful to track down performance problems as well as performance regressions over time. It would be nice if it would be easy to profile CouchDB with these tools.

coverage needs a different build, so --with-coverage makes sense.

Profiling does not need a recompilation and would best
served (IMHO) as couchdb --profile-function-calls and --profile-function-times
or however that would be integrated into the command.

couchdb --profile=function-calls --profile=function-call-times
--profile=function-fall-times-cpu or have some way to pass
options down to the profiler, you get the idea, some way of
specifying at runtime how to profile CouchDB.