Dereference remote replies (#132)

* decided where to put reply dereferencing

* fiddling with dereferencing threads

* further adventures

* tidy up some stuff

* move dereferencing functionality

* a bunch of refactoring

* go fmt

* more refactoring

* bleep bloop

* docs and linting

* start implementing replies collection on gts side

* fiddling around

* allow dereferencing our replies

* lint, fmt

docs/federation/glossary.md

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+# Glossary
+
+Some commonly-used terms in discussions of federation, and their meanings.
+
+### `ActivityPub`
+
+A decentralized social networking protocol based on the ActivityStreams data format. See [here](https://www.w3.org/TR/activitypub/).
+
+GoToSocial uses the ActivityPub protocol to communicate between GtS servers, and with other federated servers like Mastodon, Pixelfed, etc.
+
+### `ActivityStreams`
+
+A model/data format for representing potential and completed activities using JSON. See [here](https://www.w3.org/TR/activitystreams-core/).
+
+GoToSocial uses the ActivityStreams data model to 'speak' ActivityPub with other servers.
+
+### `Actor`
+
+An actor is an ActivityStreams object that is capable of performing some Activity like following, liking, creating a post, reblogging, etc. See [here](https://www.w3.org/TR/activitypub/#actors).
+
+In GoToSocial, each account/user is an actor.
+
+### `Dereference`
+
+To 'dereference' a post or a profile means to make an HTTP call to the server that hosts that post or profile, in order to obtain its ActivityStreams representation.
+
+GoToSocial 'dereferences' posts and profiles on remote servers, in order to convert them to models that GoToSocial can understand and work with.