added code copy button (#1216)

Author: jeffxtang

conf.py

@@ -55,7 +55,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['sphinx.ext.mathjax',
+extensions = ['sphinx.ext.mathjax', 'sphinx_copybutton',
               'sphinx_gallery.gen_gallery']
 
 
@@ -250,4 +250,4 @@ def setup(app):
     app.add_directive('galleryitem', GalleryItemDirective)
     app.add_directive('customgalleryitem', CustomGalleryItemDirective)
     app.add_directive('customcarditem', CustomCardItemDirective)
-    app.add_directive('customcalloutitem', CustomCalloutItemDirective)
+    app.add_directive('customcalloutitem', CustomCalloutItemDirective)

requirements.txt

@@ -2,6 +2,7 @@
 
 sphinx==1.8.2
 sphinx-gallery==0.3.1
+sphinx-copybutton
 tqdm
 numpy
 matplotlib