Connect markdown exporter to build tool

nw/core/__init__.py

@@ -6,6 +6,7 @@ from nw.core.project import NWProject
 from nw.core.spellcheck import NWSpellCheck, NWSpellEnchant, NWSpellSimple
 from nw.core.tohtml import ToHtml
 from nw.core.toodt import ToOdt
+from nw.core.tomd import ToMarkdown
 from nw.core.tools import countWords, numberToRoman, numberToWord
 
 __all__ = [
@@ -20,4 +21,5 @@ __all__ = [
     "NWSpellSimple",
     "ToHtml",
     "ToOdt",
+    "ToMarkdown",
 ]