Create a design documentation for Socket Abstraction Interface

[sgn4sangar]

Create a design document for the socket library. Just plann to create the interfaces for it. Refer to

1. db/Socket - 1
2. db/Socket - 2
3. Poco:Net

Let the Interface for this Socket be something to accept connections that can best be a file descriptor.
Support unix domain socket and vectorized io.
Take care to scale the design for tcp and tls in future.
Also, RAII object for sockets which closes the file-descriptor when it gets out of scope.