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/segmentation/plot_otsu.py

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+"""
+============
+Thresholding
+============
+
+Thresholding is used to create a binary image. This example uses Otsu's method
+to calculate the threshold value.
+
+Otsu's method calculates an "optimal" threshold (marked by a red line in the
+histogram below) by maximizing the variance between two classes of pixels,
+which are separated by the threshold. Equivalently, this threshold minimizes
+the intra-class variance.
+
+.. [1] http://en.wikipedia.org/wiki/Otsu's_method
+
+"""
+import matplotlib
+import matplotlib.pyplot as plt
+
+from skimage.data import camera
+from skimage.filters import threshold_otsu
+
+
+matplotlib.rcParams['font.size'] = 9
+
+
+image = camera()
+thresh = threshold_otsu(image)
+binary = image > thresh
+
+#fig, (ax1, ax2, ax3) = plt.subplots(1, 3, figsize=(8, 2.5))
+fig = plt.figure(figsize=(8, 2.5))
+ax1 = plt.subplot(1, 3, 1, adjustable='box-forced')
+ax2 = plt.subplot(1, 3, 2)
+ax3 = plt.subplot(1, 3, 3, sharex=ax1, sharey=ax1, adjustable='box-forced')
+
+ax1.imshow(image, cmap=plt.cm.gray)
+ax1.set_title('Original')
+ax1.axis('off')
+
+ax2.hist(image)
+ax2.set_title('Histogram')
+ax2.axvline(thresh, color='r')
+
+ax3.imshow(binary, cmap=plt.cm.gray)
+ax3.set_title('Thresholded')
+ax3.axis('off')
+
+plt.show()