Partial filtering, needs backend list support
list_filter() partially implemented
List filtering logic
Manual filter command
Track eol on buffers - changes extra-newline
Correct list writing/filtering through pipe
Enable filtering in visual mode
Merge branch 'feature/filtering'

Conflicts:
	buffer.c
	keys.c

keys.c's lambda style filter-forwarding has been removed.
A global is used instead, for now
Filter test