Add three examples for B from rosettacode.

Author: sergev

examples/doors.dub

@@ -0,0 +1,32 @@
+*name B compiler
+*       Example from rosettacode.org/wiki/100_doors#B
+*tape:7/b,40
+*library:40
+*trans-main:40020
+main()
+{
+    auto doors[100]; /* != 0 means open */
+    auto pass, door;
+
+    door = 0;
+    while (door < 100)
+        doors[door++] = 0;
+
+    pass = 0;
+    while (pass < 100) {
+        door = pass;
+        while (door < 100) {
+            doors[door] = !doors[door];
+            door = door + pass + 1;
+        }
+        ++pass;
+    }
+
+    door = 0;
+    while (door < 100) {
+        printf("door #%d is %s.*n", door+1, doors[door] ? "open" : "closed");
+        ++door;
+    }
+}
+*execute
+*end file

examples/isprime.dub

@@ -0,0 +1,31 @@
+*name B compiler
+*       Example from rosettacode.org/wiki/Primality_by_trial_division#B
+*tape:7/b,40
+*library:40
+*trans-main:40020
+isprime(n) {
+    auto p;
+
+    if (n < 2)
+        return (0);
+    if (!(n % 2))
+        return (n == 2);
+    p = 3;
+    while (n / p > p) {
+        if (!(n % p))
+            return(0);
+        p = p + 2;
+    }
+    return (1);
+}
+
+test(n) {
+    printf("%d is %s*n", n, isprime(n) ? "prime" : "not prime");
+}
+
+main() {
+    test(42);
+    test(43);
+}
+*execute
+*end file

examples/mandelbrot.b

@@ -0,0 +1,44 @@
+main() {
+    auto cx, cy, x, y, x2, y2;
+    auto iter;
+    auto xmin, xmax, ymin, ymax, maxiter, dx, dy;
+
+    xmin = -8601;
+    xmax =  2867;
+    ymin = -4915;
+    ymax =  4915;
+
+    maxiter = 32;
+
+    dx = (xmax - xmin) / 79;
+    dy = (ymax - ymin) / 24;
+
+    cy = ymin;
+    while (cy <= ymax) {
+        cx = xmin;
+        while (cx <= xmax) {
+            x = 0;
+            y = 0;
+            x2 = 0;
+            y2 = 0;
+            iter = 0;
+            while (iter < maxiter) {
+                if (x2 + y2 > 16384)
+                    break;
+
+                y = ((x * y) >> 11) + cy;
+                x = x2 - y2 + cx;
+                x2 = (x * x) >> 12;
+                y2 = (y * y) >> 12;
+                iter++;
+            }
+            putchar(' ' + iter);
+            cx = cx + dx;
+        }
+        putchar(13);
+        putchar(10);
+        cy = cy + dy;
+    }
+
+    return(0);
+}