Add option to reuse buffers for interleaved frames

[kevmo314]

Reusing buffers reduces garbage collection memory pressure. If the user opts in, the option BufferReuseEnable will reuse the payload buffer for incoming frames.

Fixes #581.

[kevmo314]

@aler9 Do you have any thoughts/feedback on this change?

[aler9]

Hello @kevmo314, while this is an improvement with respect to the current situation, it's not a complete solution. There are at least 3 methods to manage memory:

1. by using unique buffers
2. by using a shared buffer
3. by using a buffer pool

The library uses method 1 and this PR adds support for method 2, but in general users are constrained to pick one of the two methods, which is not an optimal solution, since method 1 is not efficient but method 2 prevents buffers from being shared between different routines. If we take a look at the standard Go library, that can serve as reference, most methods that require memory actually allow users to pass their own memory pointers:

type Reader interface {
	Read(p []byte) (n int, err error)
}

Therefore, a good solution consists into doing the same here, for instance by allowing users to define a callback that provides buffers:

type Server struct {
    ...
    // function used to get byte buffers
    GetBuffer func(n int) []byte
}

This behavior needs to be implemented in both server and client, with both TCP and UDP transport protocols.