modify test samples

- add spaces in filenames
- add a subdirectory

tests/sample/dir2/index.md

@@ -7,21 +7,21 @@ This is an [example link](http://example.com/ "With a Title").
 1. A list item.
 2. Another item in the list.
 
-### Images sources
+### Image sources
 
-- `768px-Hubble_Interacting_Galaxy_NGC_5257_` By NASA, ESA, the Hubble
-  Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of
-  Virginia, Charlottesville/NRAO/Stony Brook University) [Public domain], via
-  Wikimedia Commons
+- *Hubble Interacting Galaxy NGC 5257* By NASA, ESA, the Hubble Heritage
+  (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia,
+  Charlottesville/NRAO/Stony Brook University) [Public domain], via Wikimedia
+  Commons
 
-- `600px-Hubble_ultra_deep_field.jpg` Par NASA and the European Space Agency.
-  [Public domain], <a
+- *Hubble ultra deep field.jpg* Par NASA and the European Space Agency.  [Public
+  domain], <a
   href="https://commons.wikimedia.org/wiki/File%3AHubble_ultra_deep_field.jpg">via
   Wikimedia Commons</a>
 
-- `m57_the_ring_nebula-587px.jpg` By The Hubble Heritage Team
+- *m57_the_ring_nebula-587px.jpg* By The Hubble Heritage Team
   (AURA/STScI/NASA) [Public domain], <a
   href="https://commons.wikimedia.org/wiki/File%3AM57_The_Ring_Nebula.JPG">via
   Wikimedia Commons</a>
 
-- `exo20101028-b-full.jpg`
+- *exo20101028-b-full.jpg*