Fixes #8
Fixes #8

In `connection.ts`, the data cursor was not being incremented properly in the
case of a non-SB telnet command.  Instead, it was incrementing the command
data itself (e.g., `WILL TERMINAL_SPEED` became `WONT REMOTE_FLOW_CONTROL`).

This changes fixes it and adds some buffer protection.

herrevilkitten/telnet-rxjs