Add YARA language (#3877)

* Add YARA language grammars

* Add YARA to languages.yml

* Add YARA samples

* Add YARA to README

samples/YARA/OfExample.yar

@@ -0,0 +1,23 @@
+rule OfExample2
+{
+    strings:
+        $foo1 = "foo1"
+        $foo2 = "foo2"
+        $foo3 = "foo3"
+
+    condition:
+        2 of ($foo*)  // equivalent to 2 of ($foo1,$foo2,$foo3)
+}
+
+rule OfExample3
+{
+    strings:
+        $foo1 = "foo1"
+        $foo2 = "foo2"
+
+        $bar1 = "bar1"
+        $bar2 = "bar2"
+
+    condition:
+        3 of ($foo*,$bar1,$bar2)
+}