Custom Attributes File

Create the `gitbuch_custom-attributes.adoc` file for defining custom
attributes for special chars substitutions, `include::` it in the main
`gitbuch.asciidoc` source. (See #4)

docs_src/gitbuch.asciidoc

@@ -16,6 +16,8 @@ Valentin Haenel; Julius Plenz
 // :appendix-refsig: App.
 
 
+include::gitbuch_custom-attributes.adoc[]
+
 :leveloffset: +1
 
 // "vorwort.txt"          ->  Preface

docs_src/gitbuch_custom-attributes.adoc

@@ -0,0 +1,14 @@
+// *****************************************************************************
+// *                                                                           *
+// *                      CUSTOM ATTRIBUTES DEFINITIONS                        *
+// *                                                                           *
+// *****************************************************************************
+// Used for substitutions...
+
+// HTML Characters Entities
+// ========================
+// These provide human readable substitution which are safe to use on all output
+// formats (named character references are unsafe with formats like PDF)
+:en-dash: –
+
+// EOF //