add DecoderStream class, Readable stream in "objectMode"

This is replacing the old "OggStream" class since it will be just a regular
Readable stream now using the new "objectMode".
add native `ogg_packet_replace_buffer()` function

This is needed because of how Streams in node work now, in that once an
`ogg_packet` has been read() from the DecoderStream, there's no way to know when
the consumer is done with the packet. This is a problem since libogg reuses the
"packet" space of each `ogg_packet` instance each time you call
`ogg_stream_packetout()`.

The unfortunate workaround is to pass in a new node Buffer of "bytes" size after
each packetout() call, and copy over the "packet" contents to the JavaScript
buffer before we pass it off to the user.
decoder-stream: call the `ogg_packet_replace_buffer()` function
decoder-stream: add comment explaining packet_replace_buffer()
decoder-stream: remap "packet" event listeners as "data"

For backwards-compat mostly...
test: fix the decoder tests

This is an API change... now the DecoderStream instances must be consumed in
order for the Decoder to continue being consumed.
travis: don't test node v0.6.x

The old version of node-gyp there isn't compatible with node-ogg
decoder-stream: emit the "end" event
update node_pointer.h

Now has the templated UnwrapPointer() function
encoder-stream: add EncoderStream class

When you call Encoder#stream(), one of these is what's going to be returned.
encoder: incorporate the EncoderStream class

Not quite working the way it should yet...
make `node_ogg_page_to_buffer()` synchronous
remove old `stream.js` file

Was getting way too big... now separated into EncoderStream and DecoderStream
classes.
don't export the OggStream class

Since it has been deleted...
test: remove old "stream.js" tests
encoder: finish up stream2 refactor for Encoder
test: fix one of the Encoder tests
encoder: emit the "end" event

This fixes all the tests for now.
encoder: comments and tweaks