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

03_recursion/perl6/01_countdown.p6

@@ -0,0 +1,13 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+# base case
+multi countdown(0) { say 0 }
+
+# recursive case
+multi countdown($i where { $i > 0 }) {
+    say $i;
+    countdown $i-1;
+}
+
+countdown 5;

03_recursion/perl6/02_greet.p6

@@ -0,0 +1,19 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+sub greet2($name) {
+    say "how are you, $name?";
+}
+
+sub bye() {
+    say "ok bye!";
+}
+
+sub greet($name) {
+    say "hello, $name!";
+    greet2 $name;
+    say "getting ready to say bye...";
+    bye;
+}
+
+greet "adit";

03_recursion/perl6/03_factorial.p6

@@ -0,0 +1,7 @@
+#!/usr/bin/env perl6
+use v6.c;
+
+multi fact(1) { 1 }
+multi fact($x where { $x > 1 }) { $x * fact($x-1) }
+
+say fact(5);