vim-patch:8.1.0614: placing signs can be complicated

Problem:    Placing signs can be complicated.
Solution:   Add functions for defining and placing signs.  Introduce a group
            name to avoid different plugins using the same signs. (Yegappan
            Lakshmanan, closes vim/vim#3652)
162b71479b

src/nvim/eval.lua

@@ -277,6 +277,12 @@ return {
     sha256={args=1},
     shellescape={args={1, 2}},
     shiftwidth={},
+    sign_define={args={1, 2}},
+    sign_getdefined={args={0, 1}},
+    sign_getplaced={args={0, 2}},
+    sign_place={args={4, 5}},
+    sign_undefine={args={0, 1}},
+    sign_unplace={args={1, 2}},
     simplify={args=1},
     sin={args=1, func="float_op_wrapper", data="&sin"},
     sinh={args=1, func="float_op_wrapper", data="&sinh"},