implemented skeletal Buf type

The current implementation does not do anything useful, it just
adds stubbed .encode and .decode methods to Str and Buf, respectively.

build/Makefile.in

@@ -115,6 +115,7 @@ SETTING = \
   src/setting/Any-str.pm \
   src/setting/Array.pm \
   src/setting/Bool.pm \
+  src/setting/Buf.pm \
   src/setting/Hash.pm \
   src/setting/IO.pm \
   src/setting/IO/Socket.pm \
@@ -126,6 +127,7 @@ SETTING = \
   src/setting/Operators.pm \
   src/setting/Pair.pm \
   src/setting/Range.pm \
+  src/setting/Str.pm \
   src/setting/Temporal.pm \
   src/setting/Whatever.pm \
 

src/setting/Buf.pm

@@ -0,0 +1,11 @@
+class Buf does Positional {
+    method decode($encoding = 'UTF-8') {
+        return "";
+    }
+
+    method list() {
+        return [];
+    }
+}
+
+# vim: ft=perl6

src/setting/Str.pm

@@ -0,0 +1,5 @@
+class Str is also {
+    method encode($encoding = 'UTF-8', $nf = '') {
+        return Buf.new();
+    }
+}