#74 Better multiline single line support

When you have a line that is over the number of columns in a window, the line wraps. However, it isn't super obvious that the wrapped line is the same line as the first one. In GNU Emacs, they place a backslash \ at the end of the first line and continue the rest. I like this better than having the line continue into the void like how mg(1) and mle do it.

The difficulty is that the extra \ adds another character to the page which has to be accounted for when moving around. This is similar to how tab and control chars work.

Instead of adding a new character to the editor, which causes a bunch of new issues, I've decided that I'll just paint the last char on the line yellow meaning that the line wraps. I think this is an elegant solution since ait will never have a special background highlighting mode or anything.