Added some FIXME comments
First attempt to fix server HTTP request threading

- Changed server-side HTTP threading such that the connection thread calls the
  root handler instead of the root handler running in a separate thread.
- Broken: The server_streambuf instance persists across requests. The server may
  send data out-of-order to the client.
- Moved most of the server-side connection-handling template code from public
  header file to private .cpp file.
Fixed inet socket recv/send return value on error

- Fixed inet family sockets recv and send functions to return number of bytes
  successfully received or sent on error. Previously these function return 0 on
  error.
http::server_connection

Implemented (untested and unintegrated) low-level server_connection object for
managing connection with its I/O buffers.
Partial implementation of http::server_request
Broken--more server connection refactoring
Refactor complete: single-threaded HTTP server connection