TLA revisited (#2990)

* Add the TLA+ language

This patch adds support for the TLA+ specification language.

https://github.com/search?utf8=%E2%9C%93&q=MODULE+extension%3Atla&type=Code&ref=searchresults

* Update TLA grammar license

Attribution is given in the license since the grammar is based off of the TLA+ language developed by Microsoft and HP.

* Sort languages.yml alphabetically

* Removing duplicate entry

samples/TLA/AsyncInterface.tla

@@ -0,0 +1,26 @@
+--------------------------- MODULE AsyncInterface ---------------------------
+EXTENDS Naturals
+
+CONSTANT Data
+VARIABLE chan
+
+Values == <<"foo", "bar", "baz">>
+
+TypeInvariant == chan \in [val: Data, rdy: {0,1}, ack: {0,1}]
+                 
+Init == /\ TypeInvariant
+        /\ chan.ack = chan.rdy
+        
+Send(d) == /\ chan.rdy = chan.ack
+           /\ chan' = [chan EXCEPT !.val = d, !.rdy = 1 - @]
+        
+Rcv == /\ chan.rdy # chan.ack
+       /\ chan' = [chan EXCEPT !.ack = 1 - @]
+       
+Next == (\E d \in Data : Send(d)) \/ Rcv
+
+Spec == Init /\ [][Next]_chan
+
+THEOREM Spec => []TypeInvariant
+
+=============================================================================