Add other suggestions of file paths implementation

So far, v3 is my favorite.

SPECIFICATIONS.md

@@ -6,13 +6,7 @@
 
 ## Files Paths
 
-```
-<topic>[/<topic>]/chapter<NN>-<type>.<language>.<format>
-or
-<topic>[/<topic>]/<NN>-<title>-<type>.<language>.<format>
-or
-???
-```
+Let:
 
 - `topic`: lowercase alphanumeric topic name (in english, sorry)
 - `NN`: level of the course, an integer with always two digits
@@ -21,11 +15,53 @@ or
   - `textbook`
   - `cheatsheet` (?)
   - `annex`
+  - `exercises`
 
 - `language`: 2 letter lowercase language code
 - `format`: `md` for markdown
 
 
+Let's review our options, now.
+
+## Files Paths v1
+
+```
+<topic>[/<topic>]/chapter<NN>-<type>.<language>.<format>
+or
+<topic>[/<topic>]/<NN>-<title>-<type>.<language>.<format>
+or
+???
+```
+
+
+## Files Paths v2
+
+```
+<N>.<topic>[/<M>.<topic>]/<K>.<slug>/<type>.<language>.<format>
+```
+
+Each chapter gets its own directory, which will be simpler for assets organization.
+
+`01.optics/03.the-nature-of-light/textbook.fr.md`
+
+
+
+## Files Paths v3
+
+`en/01.optics/03.the-nature-of-light/textbook.md`
+
+`fr/01.optique/03.la-nature-de-la-lumiere/cahier.md`
+
+Pros:
+  - Everything
+
+Cons:
+  - Will rely on Ids, so changing them afterwards is fastidious
+    -> Can be mitigated by initially generating an empty topic dir structure
+
+-----
+
+
 ## Courses Model
 
 Each Course MUST have: