sibling 3.0.0

get next/previous sibling directory name.
Documentation
== cdnext ==
/work/testdata/basic/d (4/26)
== cdnext 3 ==
/work/testdata/basic/g (7/26)
== cdprev 2 ==
/work/testdata/basic/e (5/26)
== cdprev -1 ==
/work/testdata/basic/f (6/26)
== cdfirst ==
/work/testdata/basic/a (1/26)
== cdprev at the first ==
pwd=/work/testdata/basic/a
== cdlast ==
/work/testdata/basic/z (26/26)
== cdnext at the last ==
pwd=/work/testdata/basic/z
== lsfirst ==
/work/testdata/basic/a
== cdrand then cdfirst ==
/work/testdata/basic/a (1/26)
== spaces and multibyte ==
/work/testdata/worried/multibyte_chars_👍 (2/2)
/work/testdata/worried/dir with spaces (1/2)
== filter ==
/work/testdata/basic/e (5/26)
== filter without selection ==
pwd=/work/testdata/basic/e
== no parent ==
pwd=/
== cdnext -f list ==
/work/testdata/basic/a (1/3)
== cdnext -f list again ==
/work/testdata/basic/b (2/3)
== lsnext -f list ==
/work/testdata/basic/c
== cdnext -f list at the last ==
pwd=/work/testdata/basic/b
== nextdir / prevdir ==
/work/testdata/basic/d
/work/testdata/basic/b
== hook ==
NEXTDIR=/work/testdata/basic/f PREVDIR=/work/testdata/basic/d