Allow using the terminal emulator without a pty device.

Without a pty, connect the terminals emulator directly to stdin and
stdout/err of a process.
Use the --command switch to specify the command to start this process.
Implement simple control flow commands for the non-pty terminal.

Ctrl-C to send a SIGING and Ctrl-D to close the stdin.
Use os.read to circumvent the buffering on the Python stdout stream.