epkg-type: fix documentation

Improving the doc-string involves explicitly defining it
as a generic function.

epkg.el

@@ -385,12 +385,19 @@ is an optional dependency.
                                 :order-by [(asc package) (asc feature)]]
                                (vconcat (epkg-provided package))))))
 
-(cl-defmethod epkg-type ((pkg epkg-package))
-  "Return the type of the Epkg object PKG."
+(cl-defgeneric epkg-type (ARG)
+  "Return the type of the object or class ARG.
+
+ARG has to be the class `epkg-package', a subclass of that, an
+`epkg-package' object, or an object of a subclass.  The type
+represents the class and is used in the user interface, where
+it would be inconvenient to instead use the actual class name,
+because the latter is longer and an implementation detail.")
+
+(cl-defmethod  epkg-type ((pkg epkg-package))
   (epkg-type (eieio-object-class pkg)))
 
-(cl-defmethod epkg-type ((class (subclass epkg-package)))
-  "Return a short representation of CLASS."
+(cl-defmethod  epkg-type ((class (subclass epkg-package)))
   (if (eq class 'epkg-package)
       'all
     (setq class (symbol-name class))

epkg.org

@@ -478,14 +478,15 @@ functions return these values in a form that is generally more useful.
   that it is a mandatory dependency; if a string is used, then it
   is an optional dependency.
 
-- Function: epkg-type pkg
+- Function: epkg-type arg
 
-  This function returns the type of the ~epkg-package~ object PKG.
+  This function returns the type of the object or class ARG.
 
-  A package's type is a short representation of its class, as in
-  ~epkg-TYPE-package~.  The argument may also be a class symbol, in
-  which case the respective type is returned. The type of ~epkg-package~
-  itself is ~all~.
+  ARG has to be the class ~epkg-package~, a subclass of that, an
+  ~epkg-package~ object, or an object of a subclass.  The type
+  represents the class and is used in the user interface, where
+  it would be inconvenient to instead use the actual class name,
+  because the latter is longer and an implementation detail.
 
 - Function: epkg-package-types subtypes
 

epkg.texi

@@ -574,14 +574,15 @@ that it is a mandatory dependency; if a string is used, then it
 is an optional dependency.
 @end defun
 
-@defun epkg-type pkg
+@defun epkg-type arg
 
-This function returns the type of the @code{epkg-package} object PKG.
+This function returns the type of the object or class ARG.
 
-A package's type is a short representation of its class, as in
-@code{epkg-TYPE-package}.  The argument may also be a class symbol, in
-which case the respective type is returned. The type of @code{epkg-package}
-itself is @code{all}.
+ARG has to be the class @code{epkg-package}, a subclass of that, an
+@code{epkg-package} object, or an object of a subclass.  The type
+represents the class and is used in the user interface, where
+it would be inconvenient to instead use the actual class name,
+because the latter is longer and an implementation detail.
 @end defun
 
 @defun epkg-package-types subtypes