bring back em-dash.lua

apparently people actually use it
This reverts commit 7876e626d7.

macros/em-dash.lua

@@ -0,0 +1,27 @@
+script_name = "Em-dash"
+script_description = "I do not have an em-dash key on my keyboard"
+script_author = "garret"
+script_version = "2021-04-05"
+em = "—"
+function append(sub, sel)
+	for si, li in ipairs(sel) do
+		local line = sub[li]
+		line.text = line.text..em
+		sub[li] = line
+	end
+	aegisub.set_undo_point(script_name)
+end
+
+function replace(sub, sel)
+    for si, li in ipairs(sel) do
+        local line = sub[li]
+        local text = sub[li].text
+        text = text:gsub("%-%-",em)
+    	line.text=text
+        sub[li] = line
+    end
+	aegisub.set_undo_point(script_name)
+end
+
+aegisub.register_macro(script_name.."/Append", "Appends an Em-dash to the selected line(s)", append)
+aegisub.register_macro(script_name.."/Replace", "Replaces -- with "..em, replace)