Added feature to spawn conptyshell inside tmux session

[Thy-GoD]

It's a very small addition to the conptyshell code that allows a user to spawn the whole conptyshell thing in a another tmux pane instead.

This way, it completely removes the requirement of needing gnome-terminal and allows for more flexibility.

I might be able to figure out a way to implement this into the Linux rev shells to allow for shell upgrades.

Hope this helps.

(I am still learning and this may not be optimized code, it checks if we are inside a tmux session by checking if the tmux environment variable exists or not.)