Thinking abstractly about decode I'd expect a function signature such as:

export function decode(input: Buffer): NestedBufferList

where NestedBufferList could be any nested composition of buffers and arrays such as Buffer, or Buffer[], or [Buffer, Buffer[]], etc. (haven't tried expressing this in TS).

Currently the decode method has the following definitions:

1. First definition takes Buffer and returns a Buffer. Not sure why, it could very well be that the decoding is a NestedBufferList. This was also the problem stated in Encoding and Decoding RLP lists when part of a buffer #77
2. Second def. takes a Buffer[]. Is this to support decoding multiple serialized items simultaneously? the code doesn't seem to do that. I suggest we remove this
3. The last two take Input as argument. I imagine this is for backwards-compatibility. I suggest we tighten the API and only accept a Buffer

On the stream flag: we could keep it, or add a new function decodeStreaming.