Move out of Gitlab Wiki

I understand that this change is quite unreadable and hard to review, sorry for forgetting to do atomic commits. This patch does not change too much content wise, it just
* Gets everything from gitlab wiki
* Removes some specific gitlab hacks
* Formats all documentation file names to be in snake case so they look the same way as our code does

docs/api/differences_in_mastoapi_responses.md

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+# Differences in Mastodon API responses from vanilla Mastodon
+
+A Pleroma instance can be identified by "<Mastodon version> (compatible; Pleroma <version>)" present in `version` field in response from `/api/v1/instance` 
+
+## Flake IDs
+
+Pleroma uses 128-bit ids as opposed to Mastodon's 64 bits. However just like Mastodon's ids they are sortable strings
+
+## Attachment cap
+
+Some apps operate under the assumption that no more than 4 attachments can be returned or uploaded. Pleroma however does not enforce any limits on attachment count neither when returning the status object nor when posting.
+
+## Timelines
+
+Adding the parameter `with_muted=true` to the timeline queries will also return activities by muted (not by blocked!) users.
+
+## Statuses
+
+Has these additional fields under the `pleroma` object:
+
+- `local`: true if the post was made on the local instance.
+- `conversation_id`: the ID of the conversation the status is associated with (if any)
+
+## Attachments
+
+Has these additional fields under the `pleroma` object:
+
+- `mime_type`: mime type of the attachment.
+
+## Accounts
+
+- `/api/v1/accounts/:id`: The `id` parameter can also be the `nickname` of the user. This only works in this endpoint, not the deeper nested ones for following etc.
+
+Has these additional fields under the `pleroma` object:
+
+- `tags`: Lists an array of tags for the user
+- `relationship{}`: Includes fields as documented for Mastodon API https://docs.joinmastodon.org/api/entities/#relationship
+- `is_moderator`: boolean, true if user is a moderator
+- `is_admin`: boolean, true if user is an admin
+- `confirmation_pending`: boolean, true if a new user account is waiting on email confirmation to be activated
+
+## Notifications
+
+Has these additional fields under the `pleroma` object:
+
+- `is_seen`: true if the notification was read by the user