patch 8.1.0673: functionality for signs is spread out over several files

Problem:    Functionality for signs is spread out over several files.
Solution:   Move most of the sign functionality into sign.c. (Yegappan
            Lakshmanan, closes #3751)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 5e22470..00c4f24 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -749,6 +749,7 @@
 	$(OUTDIR)\screen.obj \
 	$(OUTDIR)\search.obj \
 	$(OUTDIR)\sha256.obj \
+	$(OUTDIR)\sign.obj \
 	$(OUTDIR)\spell.obj \
 	$(OUTDIR)\spellfile.obj \
 	$(OUTDIR)\syntax.obj \
@@ -1519,6 +1520,8 @@
 
 $(OUTDIR)/sha256.obj:	$(OUTDIR) sha256.c  $(INCL)
 
+$(OUTDIR)/sign.obj:	$(OUTDIR) sign.c  $(INCL)
+
 $(OUTDIR)/spell.obj:	$(OUTDIR) spell.c  $(INCL)
 
 $(OUTDIR)/spellfile.obj:	$(OUTDIR) spellfile.c  $(INCL)
@@ -1664,6 +1667,7 @@
 	proto/screen.pro \
 	proto/search.pro \
 	proto/sha256.pro \
+	proto/sign.pro \
 	proto/spell.pro \
 	proto/spellfile.pro \
 	proto/syntax.pro \