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/transform/plot_pyramid.py

@@ -0,0 +1,35 @@
+"""
+====================
+Build image pyramids
+====================
+
+The `pyramid_gaussian` function takes an image and yields successive images
+shrunk by a constant scale factor. Image pyramids are often used, e.g., to
+implement algorithms for denoising, texture discrimination, and scale-
+invariant detection.
+
+"""
+import numpy as np
+import matplotlib.pyplot as plt
+
+from skimage import data
+from skimage.transform import pyramid_gaussian
+
+
+image = data.astronaut()
+rows, cols, dim = image.shape
+pyramid = tuple(pyramid_gaussian(image, downscale=2))
+
+composite_image = np.zeros((rows, cols + cols / 2, 3), dtype=np.double)
+
+composite_image[:rows, :cols, :] = pyramid[0]
+
+i_row = 0
+for p in pyramid[1:]:
+    n_rows, n_cols = p.shape[:2]
+    composite_image[i_row:i_row + n_rows, cols:cols + n_cols] = p
+    i_row += n_rows
+
+fig, ax = plt.subplots()
+ax.imshow(composite_image)
+plt.show()