gparam: Tidy up property naming documentation

There’s no need to have the property naming documentation in two places,
with one version of it being stricter than the other. Rationalise it to
one place, link to that consistently, and settle on the stricter
version.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #358

gobject/gparam.c

@@ -41,11 +41,14 @@
  *
  * ## Parameter names # {#canonical-parameter-names}
  *
- * Parameter names need to start with a letter (a-z or A-Z).
- * Subsequent characters can be letters, numbers or a '-'.
- * All other characters are replaced by a '-' during construction.
- * The result of this replacement is called the canonical name of
- * the parameter.
+ * A property name consists of segments consisting of ASCII letters and
+ * digits, separated by either the `-` or `_` character. The first
+ * character of a property name must be a letter. These are the same rules as
+ * for signal naming (see g_signal_new()).
+ *
+ * When creating and looking up a #GParamSpec, either separator can be
+ * used, but they cannot be mixed. Using `-` is considerably more
+ * efficient, and is the ‘canonical form’. Using `_` is discouraged.
  */
 
 
@@ -401,15 +404,9 @@ is_canonical (const gchar *key)
  *
  * Creates a new #GParamSpec instance.
  *
- * A property name consists of segments consisting of ASCII letters and
- * digits, separated by either the '-' or '_' character. The first
- * character of a property name must be a letter. Names which violate these
- * rules lead to undefined behaviour.
- *
- * When creating and looking up a #GParamSpec, either separator can be
- * used, but they cannot be mixed. Using '-' is considerably more
- * efficient and in fact required when using property names as detail
- * strings for signals.
+ * See [canonical parameter names][canonical-parameter-names] for details of
+ * the rules for @name. Names which violate these rules lead to undefined
+ * behaviour.
  *
  * Beyond the name, #GParamSpecs have two more descriptive
  * strings associated with them, the @nick, which should be suitable