Reduce Unnecessary Allocations

[nickajacks1]

In profiling my application, I noticed that packets.ReadPacket was making extra unnecessary allocations by calling io.CopyN (which internally allocates its own temporary buffer). In this example, we can just call r.Read to eliminate that extra allocation. I would like to comb through the code (or at least the codepaths my applications use :) ) and see if there are any other low hanging fruit as well.

(I'm making this issue as somewhat of a formality since the PR template says to open an issue first.)

[MattBrittan]

Thanks - the template requests an issue first to avoid committers doing work that's unlikely to be accepted (based on a misunderstanding, or not in line with the project philisophy). Prefer to have a quick chat first, particularly if it's a big change.

Based on a quick look I think that what you are proposing makes sense. Remember that Read may return less data than requested (and a nil errror) so a loop will be needed. I'm not really focused on performance (as it's not been an issue for me) so do rely on others for this kind of optomisation).