Add `weechat-buffer-line-limit' and truncate when reaching this limit.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Update TODO.org (M)

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Merge branch 'master' into limit-bufsize

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