Add optional 'compression' argument.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Use `forward-line' with neg. arg instead of `previous-line'.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
weechat-corrector: Handle nil text.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>