Warn on unused bindings (strict lint).

This does create a lot of warnings, especially in the test suite, but
should improve code and point out real issues.

To disable individual messages, either disable linting, add the metadata :unused to a
binding, or add the prefix "_" to a symbol.

examples/chatserver.janet

@@ -26,7 +26,7 @@
           (broadcast name (string msg)))
         (print name " disconnected")))))
 
-(defn main [& args]
+(defn main [&]
   (printf "STARTING SERVER...")
   (flush)
   (def my-server (net/listen "127.0.0.1" "8000"))

examples/debugger.janet

@@ -132,7 +132,7 @@
   "Go to the next breakpoint."
   [&opt n]
   (var res nil)
-  (for i 0 (or n 1)
+  (repeat (or n 1)
     (set res (resume (.fiber))))
   res)
 
@@ -146,6 +146,6 @@
   "Execute the next n instructions."
   [&opt n]
   (var res nil)
-  (for i 0 (or n 1)
+  (repeat (or n 1)
     (set res (debug/step (.fiber))))
   res)

examples/rtest.janet

@@ -2,7 +2,7 @@
 
 (def counts (seq [_ :range [0 100]] 0))
 
-(for i 0 1000000
+(repeat 1000000
   (let [x (math/random)
         intrange (math/floor (* 100 x))
         oldcount (counts intrange)]

examples/threaded-channels.janet

@@ -7,7 +7,7 @@
   (ev/give chan (math/random))
   (ev/give chan (math/random))
   (ev/sleep 0.5)
-  (for i 0 10
+  (repeat 10
     (print "giving to channel...")
     (ev/give chan (math/random))
     (ev/sleep 1))