allow inserting line breaks in the mud client text input

[OliverLSanz]

I have noticed you can't send a multiline message using the client. The enter button sends the message, which is fine, but It would be good to be able to use shift+enter to insert a new line.

I've also noticed that if you copy some text with line breaks and you paste it into the client input the line breaks get replaced by whitespaces.

My use case for this is the game I'm developing where users may enter descriptions for items or rooms they create. Splitting the message in different lines is great to make the descriptions more readable. I believe it would be useful for other games too.