add perl6 code for chapters 1-4 (#49)

01_introduction_to_algorithms/perl6/01_binary_search.p6

@@ -0,0 +1,35 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+sub binary-search(@arr, $item){
+    # low and high keep track of which part of the array you'll search in.
+    my $low = 0;
+    my $high = @arr.elems - 1;
+
+    # While you haven't narrowed it down to one element ...
+    while $low <= $high {
+        # ... check the middle element
+        my $mid = ($low + $high) div 2;
+        my $guess = @arr[$mid];
+        # Found the item.
+        if $guess ~~ $item {
+            return $mid;
+        }
+        # The guess was too high.
+        if $guess > $item {
+            $high = $mid - 1;
+        }
+        # The guess was too low.
+        else {
+            $low = $mid + 1;
+        }
+    }
+    # Item doesn't exist
+    return Nil;
+}
+
+my @arr = 1, 3, 5, 7, 9;
+say binary-search(@arr, 3); # => 1
+
+# We use 'Nil' to indicate that the item wasn't found.
+say binary-search(@arr, -1); # => Nil