Add tasks for all the new languages

Task/Extensible-prime-generator/EchoLisp/extensible-prime-generator.echolisp

@@ -0,0 +1,35 @@
+; the first twenty primes
+(primes 20)
+    → { 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 }
+
+; a stream to generate primes from a
+(define (primes-from a)
+    (let ((p (next-prime a)))
+     (stream-cons p (primes-from p))))
+
+; primes between 100,150
+(for/list  ((p (primes-from 100)))  #:break  (> p 150) p)
+    → (101 103 107 109 113 127 131 137 139 149)
+
+; the built-in function (primes-pi )counts the number of primes < a
+; count in [7700 ...  8000]
+(- (primes-pi 8000) (primes-pi 7700) → 30
+
+; nth-prime
+(nth-prime 10000) → 104729
+
+;; big ones
+(lib 'bigint)
+(define (p-digits n)
+  (printf "(next-prime  %d ! ) has %d digits" n
+  (number-length (next-prime (factorial n )))))
+
+(next-prime 0! ) has 1 digits
+(next-prime 10! ) has 7 digits
+(next-prime 100! ) has 158 digits
+(next-prime 200! ) has 375 digits
+(next-prime 300! ) has 615 digits
+(next-prime 400! ) has 869 digits ;; 9400 msec (FireFox)
+
+; is prime (1 + 116!) ?
+(prime? (1+ (factorial 116)))  → #t