New doc section: codesnippets / Advanced Examples

Presents code examples that use the instaloader module for more advanced tasks
than what is possible with the Instaloader command line interface.

Presents #46, #56, #110, #113, #120, #121.

docs/codesnippets/56_track_deleted.py

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+from glob import glob
+from sys import argv
+from os import chdir
+
+from instaloader import Instaloader, Post, Profile, load_structure_from_file
+
+# Instaloader instantiation - you may pass additional arguments to the constructor here
+L = Instaloader()
+
+# If desired, load session previously saved with `instaloader -l USERNAME`:
+#L.load_session_from_file(USERNAME)
+
+try:
+    TARGET = argv[1]
+except IndexError:
+    raise SystemExit("Pass profile name as argument!")
+
+# Obtain set of posts that are on hard disk
+chdir(TARGET)
+offline_posts = set(filter(lambda s: isinstance(s, Post),
+                           (load_structure_from_file(L.context, file)
+                            for file in (glob('*.json.xz') + glob('*.json')))))
+
+# Obtain set of posts that are currently online
+post_iterator = Profile.from_username(L.context, TARGET).get_posts()
+online_posts = set(post_iterator)
+
+if online_posts - offline_posts:
+    print("Not yet downloaded posts:")
+    print(" ".join(str(p) for p in (online_posts - offline_posts)))
+
+if offline_posts - online_posts:
+    print("Deleted posts:")
+    print(" ".join(str(p) for p in (offline_posts - online_posts)))