Added sections to gallery of examples

Modified travis_script.sh to account for the new structure of the gallery

Added README.txt files in directories of gallery examples

Fixed references to gallery images in user guide pages

Fixed broken links

doc/examples/edges/plot_convex_hull.py

@@ -0,0 +1,53 @@
+"""
+===========
+Convex Hull
+===========
+
+The convex hull of a binary image is the set of pixels included in the
+smallest convex polygon that surround all white pixels in the input.
+
+In this example, we show how the input pixels (white) get filled in by the
+convex hull (white and grey).
+
+A good overview of the algorithm is given on `Steve Eddin's blog
+<http://blogs.mathworks.com/steve/2011/10/04/binary-image-convex-hull-algorithm-notes/>`__.
+
+"""
+import numpy as np
+import matplotlib.pyplot as plt
+
+from skimage.morphology import convex_hull_image
+
+
+image = np.array(
+    [[0, 0, 0, 0, 0, 0, 0, 0, 0],
+     [0, 0, 0, 0, 1, 0, 0, 0, 0],
+     [0, 0, 0, 1, 0, 1, 0, 0, 0],
+     [0, 0, 1, 0, 0, 0, 1, 0, 0],
+     [0, 1, 0, 0, 0, 0, 0, 1, 0],
+     [0, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=float)
+
+original_image = np.copy(image)
+
+chull = convex_hull_image(image)
+image[chull] += 1
+# image is now:
+# [[ 0.  0.  0.  0.  0.  0.  0.  0.  0.]
+#  [ 0.  0.  0.  0.  2.  0.  0.  0.  0.]
+#  [ 0.  0.  0.  2.  1.  2.  0.  0.  0.]
+#  [ 0.  0.  2.  1.  1.  1.  2.  0.  0.]
+#  [ 0.  2.  1.  1.  1.  1.  1.  2.  0.]
+#  [ 0.  0.  0.  0.  0.  0.  0.  0.  0.]]
+
+
+fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(10, 6))
+
+ax1.set_title('Original picture')
+ax1.imshow(original_image, cmap=plt.cm.gray, interpolation='nearest')
+ax1.set_xticks([]), ax1.set_yticks([])
+
+ax2.set_title('Transformed picture')
+ax2.imshow(image, cmap=plt.cm.gray, interpolation='nearest')
+ax2.set_xticks([]), ax2.set_yticks([])
+
+plt.show()