Added `union`, `short` and `long` keywords to .c syntax

data/core/syntax.lua

@@ -106,6 +106,7 @@ syntax.add {
     ["return"]   = "keyword",
     ["goto"]     = "keyword",
     ["struct"]   = "keyword",
+    ["union"]    = "keyword",
     ["typedef"]  = "keyword",
     ["enum"]     = "keyword",
     ["extern"]   = "keyword",
@@ -120,6 +121,8 @@ syntax.add {
     ["const"]    = "keyword",
     ["void"]     = "keyword",
     ["int"]      = "keyword2",
+    ["short"]    = "keyword2",
+    ["long"]     = "keyword2",
     ["float"]    = "keyword2",
     ["double"]   = "keyword2",
     ["char"]     = "keyword2",