Tweak IterationBuffer documentation a bit

After having written tests, I noticed some properties were missing

Author: lizmat

doc/Type/IterationBuffer.rakudoc

@@ -29,38 +29,40 @@ argument which, when specified, will be used to fill the C<IterationBuffer>.
 
     method push(IterationBuffer:D: Mu \value)
 
-Adds the given value at the end of the C<IterationBuffer>.
+Adds the given value at the end of the C<IterationBuffer> and returns the
+given value.
 
 =head2 method unshift
 
     method unshift(IterationBuffer:D: Mu \value)
 
-Adds the given value at the beginning of the C<IterationBuffer>.
+Adds the given value at the beginning of the C<IterationBuffer> and returns
+the given value.
 
 =head2 method append
 
-    method append(IterationBuffer:D: IterationBuffer:D $other)
+    method append(IterationBuffer:D: IterationBuffer:D $other --> IterationBuffer:D)
 
 Adds the contents of the other C<IterationBuffer> at the end of
-the C<IterationBuffer>.
+the C<IterationBuffer>, and returns the updated invocant.
 
 =head2 method prepend
 
-    method prepend(IterationBuffer:D: IterationBuffer:D $other)
+    method prepend(IterationBuffer:D: IterationBuffer:D $other --> IterationBuffer:D)
 
 Adds the contents of the other C<IterationBuffer> at the beginning
-of the C<IterationBuffer>.
+of the C<IterationBuffer>, and returns the updated invocant.
 
 =head2 method clear
 
-    method clear(IterationBuffer:D:)
+    method clear(IterationBuffer:D: --> Nil)
 
 Resets the number of elements in the C<IterationBuffer> to zero,
-effectively removing all data from it.
+effectively removing all data from it, and returns C<Nil>.
 
 =head2 method elems
 
-    method elems(IterationBuffer:D:)
+    method elems(IterationBuffer:D: --> Int:D)
 
 Returns the number of elements in the C<IterationBuffer>.
 
@@ -87,25 +89,25 @@ negative position values.
 
 =head2 method Slip
 
-    method Slip(IterationBuffer:D:)
+    method Slip(IterationBuffer:D: --> Slip:D)
 
 Coerces the C<IterationBuffer> to a L<Slip|/type/Slip>.
 
 =head2 method List
 
-    method List(IterationBuffer:D:)
+    method List(IterationBuffer:D: --> List:D)
 
 Coerces the C<IterationBuffer> to a L<List|/type/List>.
 
 =head2 method Seq
 
-    method Seq(IterationBuffer:D:)
+    method Seq(IterationBuffer:D: --> Seq:D)
 
 Coerces the C<IterationBuffer> to a L<Seq|/type/Seq>.
 
 =head2 method raku
 
-    method raku(IterationBuffer:D:)
+    method raku(IterationBuffer:D: --> Str)
 
 Produces a representation of the C<IterationBuffer> as a C<List>
 postfixed with ".IterationBuffer" to make it different from an