In the old code `sending` in the `send()` method shared the Data slice's
underlying backing array with its caller. Clearing StreamFrame.Data
didn't break the reference from the sent frame to the StreamFramer's
data slice.
According to go/codec's docs, Reset(...) should be called on
Decoders/Encoders before reuse:
https://godoc.org/github.com/ugorji/go/codec
I could find no evidence that *not* calling Reset() caused bugs, but
might as well do what the docs say?
