feature request: split objectMode into readableObjectMode and writableObjectMode

[jonathanong]

http://nodejs.org/api/stream.html#stream_state_objects

basically, the docs say "don't touch the stream states except to set explicit object modes". why not have readableObjectMode and writableObjectMode options in addition to objectMode so you can just get rid of this whole section?

for example, in WritableState, we can do:

this.objectMode = !!(options.writableObjectMode || options.objectMode)

[manuelsantillan]

+1.
For us who are using "userland" streams and working on object mode streams, we find that object mode does not "feel right". This is one example, because you usually have incoming data in buffer/string mode that at some point gets transformed to objects and we need to adapt it. Conversely, when outputing data the conversion is the other way round.

Another quirk for "object mode" is the issue #6594

These kind of problems make it hard to apply "middleware-like" integration patterns in our code (routers, pub/sub, ...) like you would apply for example with apache camel or mule.