Bump version to 0.4.0

Changes since 0.3.0:
 * New `@setting name` block directive to declare global and per-buffer
   settings.
 * Fix and document `@all` directive.
 * Make id for `@section name[, id]` block directive truly optional.
 * Document `@subsection name` and `@backmatter id`.

Author: dbarnett

setup.py

@@ -3,7 +3,7 @@
 
 setup(
     name='vimdoc',
-    version='0.3.0',
+    version='0.4.0',
     description='Generate vim helpfiles',
     author='Nate Soares',
     author_email='[email protected]',