Move TelnetParser code to subdirectory telnet
New enum TelnetCommand

Added new enum TelnetCommand that represents the TELNET command codes
defined in RFC 854.
TelnetParser doesn't emit dataReceived for commands

TelnetParser class does not emit dataReceived() signal for TELNET
commands.
New enum TelnetOption

Added new enum TelnetOption that represents TELNET option codes defined
in several RFCs.
TelnetParser emits optionNegotiationReceived

The TelnetParser class emits the signal optionNegotiationReceived()
when it parsed a single option command.
Move command parsing into separate method

Refactor TelnetParser by moving the option command parsing from
parse() into a separate parseCommand() method.
TelnetParser handles multiple option commands

The TelnetParser class can now handle multiple option negotiations
in the data buffer.