Break NLP tutorial into parts

Author: chsasank

.gitignore

@@ -6,8 +6,13 @@ advanced
 #data things
 beginner_source/hymenoptera_data
 intermediate_source/data/
+advanced_source/images/
 *data.zip
 
+#builds
+_build/
+_static/thumbs/
+
 # Byte-compiled / optimized / DLL files
 __pycache__/
 *.py[cod]