More synchronization patterns with `GroupedInput`:
 - 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.
 - New options: `sendStreams` and `receiveStreams` which allow reading and writing substreams as atomic tree-like structures.
 - Added `load` counters for `async` processes.
 - Added support for grouping multiple output ports. This is useful when a component sends data to one ore more outputs per invokation. The order between inputs and outputs can still be preserved with `ordered` option.
 - Fixes and updates in the specs.
Omit `load` counter if outport is missing.
Updated `CHANGES`.
`CustomError` and `MultiError` helpers and specs for #185
Updated `CHANGES`
Merge pull request #188 from trustmaster/master

More patterns with `GroupedInput` and `MultiError`