Add telnet support

[tom0010]

I don't see any reference to telnet support in the code. It would be good if you could add it.
I regularly use telnet to test connections/and my code in an emulated env (using eve-ng).
Currently I've been using Netmiko, which supports this, I would love it if you could add the support in.
Thanks.

[selfuryon]

Hello, @t1hom7as!
Right now netdev is based upon asyncssh, and it supports only ssh. At the start of writing this library, no implementation of async telnet had existed.
But right now I see that one implementation exists: telnetlib3. I will plan to implement it, thank you!

[tom0010]

Hello, @t1hom7as!
Right now netdev is based upon asyncssh, and it supports only ssh. At the start of writing this library, no implementation of async telnet had existed.
But right now I see that one implementation exists: telnetlib3. I will plan to implement it, thank you!

Ok great - I look forward to it!

[vsrx6]

This is an excellent library! I really hope telnet support gets added soon.

[Ali-aqrabawi]

i'm interested to work on this, you can assign it to me

[selfuryon]

Related PR #33