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_join_segmentations.py

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+"""
+==========================================
+Find the intersection of two segmentations
+==========================================
+
+When segmenting an image, you may want to combine multiple alternative
+segmentations. The `skimage.segmentation.join_segmentations` function
+computes the join of two segmentations, in which a pixel is placed in
+the same segment if and only if it is in the same segment in _both_
+segmentations.
+
+"""
+import numpy as np
+from scipy import ndimage as ndi
+import matplotlib.pyplot as plt
+
+from skimage.filters import sobel
+from skimage.segmentation import slic, join_segmentations
+from skimage.morphology import watershed
+from skimage.color import label2rgb
+from skimage import data, img_as_float
+
+coins = img_as_float(data.coins())
+
+# make segmentation using edge-detection and watershed
+edges = sobel(coins)
+markers = np.zeros_like(coins)
+foreground, background = 1, 2
+markers[coins < 30.0 / 255] = background
+markers[coins > 150.0 / 255] = foreground
+
+ws = watershed(edges, markers)
+seg1 = ndi.label(ws == foreground)[0]
+
+# make segmentation using SLIC superpixels
+seg2 = slic(coins, n_segments=117, max_iter=160, sigma=1, compactness=0.75,
+            multichannel=False)
+
+# combine the two
+segj = join_segmentations(seg1, seg2)
+
+# show the segmentations
+fig, axes = plt.subplots(ncols=4, figsize=(9, 2.5), sharex=True, sharey=True, subplot_kw={'adjustable':'box-forced'})
+axes[0].imshow(coins, cmap=plt.cm.gray, interpolation='nearest')
+axes[0].set_title('Image')
+
+color1 = label2rgb(seg1, image=coins, bg_label=0)
+axes[1].imshow(color1, interpolation='nearest')
+axes[1].set_title('Sobel+Watershed')
+
+color2 = label2rgb(seg2, image=coins, image_alpha=0.5)
+axes[2].imshow(color2, interpolation='nearest')
+axes[2].set_title('SLIC superpixels')
+
+color3 = label2rgb(segj, image=coins, image_alpha=0.5)
+axes[3].imshow(color3, interpolation='nearest')
+axes[3].set_title('Join')
+
+for ax in axes:
+    ax.axis('off')
+fig.subplots_adjust(hspace=0.01, wspace=0.01, top=1, bottom=0, left=0, right=1)
+plt.show()