[FIX] project-specific static files

Turns out exclude_patterns is used when looking for markup source
files but also when looking for HTML static files, which is noted in
the documentation but apparently not in the sample conf.py

Don't exclude_patterns _-prefixed directories, or _static isn't copied
and a bunch of images and JS files break.

conf.py

@@ -73,8 +73,6 @@ today_fmt = '%B %d, %Y'
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 exclude_patterns = [
-    # build, extensions, statics, templates
-    '_*',
     # translations
     'locale',
     'README.*',