RFC: Eval scope 

As a replacement for #7 . I think this is a slightly cleaner/simpler solution. 

@timholy @rened : Thoughts? We can merge #7 if you don't like this. 

Thanks to @timholy for discovering the trick to get current module. 

```jlcon
julia> function tst(a); return a*2; end
# method added to generic function tst

julia> require("ZMQ/src/RPCJuliaSer"); using RPCJuliaSer; run_server()
```

```jlcon
julia> require("ZMQ/src/RPCJuliaSer"); using RPCJuliaSer; c,r = launch_client()
(ZMQContext(Ptr{Void} @0x00000001038a03f0),ZMQSocket(Ptr{Void} @0x000000010389c0e0))

julia> zmqcall(r, :tst, 2)
4
```