Add tasks for all the new languages

Task/Stern-Brocot-sequence/EchoLisp/stern-brocot-sequence-1.echolisp

@@ -0,0 +1,9 @@
+;; stern (2n ) = stern (n)
+;; stern(2n+1) = stern(n) + stern(n+1)
+
+(define (stern n)
+	(cond
+		(( < n 3) 1)
+		((even? n) (stern (/ n 2)))
+		(else (let ((m (/ (1- n) 2))) (+ (stern m) (stern (1+ m)))))))
+(remember 'stern)

Task/Stern-Brocot-sequence/EchoLisp/stern-brocot-sequence-2.echolisp

@@ -0,0 +1,20 @@
+; generate the sequence and check GCD
+(for ((n 10000))
+    (unless (= (gcd (stern n) (stern (1+ n))) 1) (error "BAD GCD" n)))
+    → #t
+
+;; first items
+(define sterns (cache 'stern))
+(subvector sterns 1 16)
+   → #( 1 1 2 1 3 2 3 1 4 3 5 2 5 3 4)
+
+;; first occurences index
+(for ((i (in-range 1 11))) (write (vector-index i sterns)))
+→  0 3 5 9 11 33 19 21 35 39
+
+;; 100
+(writeln (vector-index 100 sterns))
+→ 1179
+
+(stern 900000) → 446
+(stern 900001) → 2479

Task/Stern-Brocot-sequence/EchoLisp/stern-brocot-sequence-3.echolisp

@@ -0,0 +1,13 @@
+;; grouping
+(for ((i (in-range 2 40 2))) (write (/ (stern i)(stern (1+ i)))))
+→ 1/2 1/3 2/3 1/4 3/5 2/5 3/4 1/5 4/7 3/8 5/7 2/7 5/8 3/7 4/5 1/6 5/9 4/11 7/10
+
+;; computing f(1), f(f(1)), etc.
+(define (f x)
+    (let [(a (/ (- (floor x) -1 (fract x))))]
+    (if (> a 1) (f a) (cons a a))))
+
+(define T (make-stream f 1))
+(for((i 19)) (write (stream-iterate T)))
+
+→  1/2 1/3 2/3 1/4 3/5 2/5 3/4 1/5 4/7 3/8 5/7 2/7 5/8 3/7 4/5 1/6 5/9 4/11 7/10