Reducing memory allocations for receiving data

[joreg]

For both Client and Server:

Changes:

• The internal receive buffer is now only allocated once

Breaking Change:

• MessageReceivedEventArgs now returns an ArraySegment that directly refers to the internal MemoryStream, saving an extra allocation for each receive

[jchristn]

Thank you @joreg sorry for the delay in integrating this.

Commit: https://github.com/jchristn/WatsonWebsocket/commit/4a18d093836420c4d966bf3361d5f13e91f497f3 NuGet: https://www.nuget.org/packages/WatsonWebsocket/3.0.1