Add development section

* I cretaed a folder 'development'
* I split up the file dev.md into three parts and moved it to this folder
  * index.md
  * authentication_authorization.md
  * mrf.md
* I also moved ap_extensions.md
* I created a new file setting_up_pleroma_dev.md

docs/development/ap_extensions.md

@@ -0,0 +1,65 @@
+# AP Extensions
+## Actor endpoints
+
+The following endpoints are additionally present into our actors.
+
+- `oauthRegistrationEndpoint` (`http://litepub.social/ns#oauthRegistrationEndpoint`)
+- `uploadMedia` (`https://www.w3.org/ns/activitystreams#uploadMedia`)
+
+### oauthRegistrationEndpoint
+
+Points to MastodonAPI `/api/v1/apps` for now.
+
+See <https://docs.joinmastodon.org/methods/apps/>
+
+### uploadMedia
+
+Inspired by <https://www.w3.org/wiki/SocialCG/ActivityPub/MediaUpload>, it is part of the ActivityStreams namespace because it used to be part of the ActivityPub specification and got removed from it.
+
+Content-Type: multipart/form-data
+
+Parameters:
+- (required) `file`: The file being uploaded
+- (optionnal) `description`: A plain-text description of the media, for accessibility purposes.
+
+Response: HTTP 201 Created with the object into the body, no `Location` header provided as it doesn't have an `id`
+
+The object given in the reponse should then be inserted into an Object's `attachment` field.
+
+## ChatMessages
+
+`ChatMessage`s are the messages sent in 1-on-1 chats. They are similar to
+`Note`s, but the addresing is done by having a single AP actor in the `to`
+field. Addressing multiple actors is not allowed. These messages are always
+private, there is no public version of them. They are created with a `Create`
+activity.
+
+They are part of the `litepub` namespace as `http://litepub.social/ns#ChatMessage`.
+
+Example:
+
+```json
+{
+  "actor": "http://2hu.gensokyo/users/raymoo",
+  "id": "http://2hu.gensokyo/objects/1",
+  "object": {
+    "attributedTo": "http://2hu.gensokyo/users/raymoo",
+    "content": "You expected a cute girl? Too bad.",
+    "id": "http://2hu.gensokyo/objects/2",
+    "published": "2020-02-12T14:08:20Z",
+    "to": [
+      "http://2hu.gensokyo/users/marisa"
+    ],
+    "type": "ChatMessage"
+  },
+  "published": "2018-02-12T14:08:20Z",
+  "to": [
+    "http://2hu.gensokyo/users/marisa"
+  ],
+  "type": "Create"
+}
+```
+
+This setup does not prevent multi-user chats, but these will have to go through
+a `Group`, which will be the recipient of the messages and then `Announce` them
+to the users in the `Group`.