Integrate new parser which parses redis protocol

Features

Move reading of stream up from client_input.read_input() to handle_connection_helper().
In handle_connection(), wait for more input if input is incomplete send error response and break out of the loop.
In ParsedCommand, remove num_args_in_input, change args from Option<Vec to Vec.
Added an AppError to handle all the errors that may result from the program.

What's Changed

• Feature/integrate new parser by @hanchiang in #3

Full Changelog: 0.2.0...0.3.0