Removing traling spaces from end of lines.

[amshali]

This is useful because when one is copying lines from term.js all those   characters are also copied and what you will see when you paste is a bunch of useless spaces which are usually undesired. This patch fixes this issue by removing traling spaces when we are constructing the lines. There is a caveat for empty lines. We need to leave at least one space there or otherwise the output will lose lines.

[amshali]

@chjj Could you please take a look at this? Thanks a bunch.

[amshali]

@chjj That would be great if you could look at this. Thanks.