Add YARA language (#3877)

* Add YARA language grammars

* Add YARA to languages.yml

* Add YARA samples

* Add YARA to README

samples/YARA/example.yara

@@ -0,0 +1,13 @@
+rule silent_banker : banker
+{
+    meta:
+        description = "This is just an example"
+        thread_level = 3
+        in_the_wild = true
+    strings:
+        $a = {6A 40 68 00 30 00 00 6A 14 8D 91}
+        $b = {8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9}
+        $c = "UVODFRYSIHLNWPEJXQZAKCBGMT"
+    condition:
+        $a or $b or $c
+}