parameters to the callback, `strbuf_expand()` passes a context pointer,
which can be used by the programmer of the callback as she sees fit.
+`strbuf_expand_dict_cb`::
+
+ Used as callback for `strbuf_expand()`, expects an array of
+ struct strbuf_expand_dict_entry as context, i.e. pairs of
+ placeholder and replacement string. The array needs to be
+ terminated by an entry with placeholder set to NULL.
+
`strbuf_addf`::
Add a formatted string to the buffer.