docs+build: Prepare release of version 0.4.0

Change-Id: Ie5dfb3a1c7674cd426b89721c91ad59327517764
Refs: #3178
diff --git a/src/lp/detail/field-decl.hpp b/src/lp/detail/field-decl.hpp
index 3461906..02a3677 100644
--- a/src/lp/detail/field-decl.hpp
+++ b/src/lp/detail/field-decl.hpp
@@ -132,6 +132,7 @@
   }
 
   /** \brief encodes a field and prepends to \p encoder its Block with top-level type \p TYPE
+   *  \param encoder Instance of the buffer encoder or buffer estimator
    *  \param value value of the field
    */
   template<typename encoding::Tag TAG, typename T>