More synchronization patterns with `GroupedInput`:

Changes:
 - Made `group` and `forwardGroups` options orthogonal, so `forwardGroups` isn't enabled by default if `group` is on. Make sure to update your `0.5.2` code if you used `group` to forward groups from input to output.
 - New options: `sendStreams` and `receiveStreams` which allow reading and writing substreams as atomic tree-like structures. See `should support complex substreams` in `spec/Helpers.coffee` for example.
 - Added `load` counter outport support for `async` processes.
 - Added support for grouping multiple output ports. This is useful when a component sends data to one ore more outputs per invocation. The order between inputs and outputs can still be preserved with `ordered` option. See `when there are multiple output routes` spec in `spec/Helpers.coffee`.
 - Fixes and updates in the specs.