Done Unix-like clear screen keystroke command.

[mfarah]

On Unix shells, ^L clears the screen. In TCC, this can be emulated with a Q&D alias like this:

@@^L=cls

... except it misses one thing: on Unix shells, whatever the command line had contained it's preserved and the user can keep editing it. Here, instead, the cls command is added to whatever the user had written in the first place, executing that command with an added "cls" as an (obviously wrong) argument. I'd like to have a keystroke command that duplicates the way the Unix shells clear the screen with ^L (which I'll then map to... ^L).