fix repl freezing when typing C-<arrows>

[matteoeghirotta]

I made some changes to solve the problem of repl freezing when typing Ctrl-right/left arrow. I'm used to these key bindings in emacs and muscle memory makes linedit unusable for me, since the terminal suddenly becomes unresponsive. I bound C-right to forward-sexp and C-left to backward-sexp. I also added the clear-screen (screen refresh as in emacs) command (bound to C-l) and new-sexp (bound to M-N)

[matteoeghirotta]

I should add that I'm on linux (debian), don't know how my changes affect mac users