Gnuplot Syntax highlighting (#2483)

* gnuplot syntax support

* Update gnuplot.yaml

* Add files via upload

* Update gnuplot.yaml

runtime/syntax/gnuplot.yaml

@@ -0,0 +1,15 @@
+filetype: gnuplot
+
+detect:
+    filename: "\\.(gnu|gpi|plt|gp)$"
+
+rules:
+    - statement: "\\b(set|unset|plot|splot|replot|if|else|do|for|while|fit)\\b"
+    - symbol.operator: "[-+/*=<>?:!~%&|^$]"
+    - constant.number: "\\b([0-9]+|0x[0-9a-fA-F]*)\\b"
+    
+    - comment:
+        start: "#"
+        end: "$"
+        rules:
+            - todo: "TODO:?"