interest+data: add string_view overloads for convenience

Also, explicitly declare the nullptr_t overloads as deleted, so that
users get a clear compilation error instead of a potentially confusing
"ambiguous overload" if they try to pass nullptr to these functions.

Change-Id: I399efcbd698a0d3f7e29219d21eb1a53a1d71070
diff --git a/docs/examples.rst b/docs/examples.rst
index a778b25..a2a0a0c 100644
--- a/docs/examples.rst
+++ b/docs/examples.rst
@@ -41,7 +41,7 @@
 .. literalinclude:: ../examples/producer.cpp
    :language: c++
    :linenos:
-   :emphasize-lines: 39-42,55,62-64,79,87,91
+   :emphasize-lines: 39-42,55,60-63,78,86,90
 
 Consumer that uses Scheduler
 ----------------------------