refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/xanthous/src/Xanthous/Entities/Marker.hs

@@ -0,0 +1,41 @@
+--------------------------------------------------------------------------------
+module Xanthous.Entities.Marker ( Marker(..) ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude
+--------------------------------------------------------------------------------
+import           Data.Aeson
+import           Test.QuickCheck
+import qualified Graphics.Vty.Attributes as Vty
+import qualified Graphics.Vty.Image as Vty
+import           Brick.Widgets.Core (raw)
+--------------------------------------------------------------------------------
+import           Xanthous.Game.State
+import           Xanthous.Data.Entities (EntityAttributes(..))
+--------------------------------------------------------------------------------
+
+-- | Mark on the map - for use in debugging / development only.
+newtype Marker = Marker Text
+  deriving stock (Show, Eq, Ord, Generic)
+  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving (Semigroup, Monoid, ToJSON, FromJSON, Arbitrary) via Text
+
+instance Brain Marker where step = brainVia Brainless
+
+instance Entity Marker where
+  entityAttributes = const EntityAttributes
+    { _blocksVision = False
+    , _blocksObject = False
+    , _collision = Stop
+    }
+  description (Marker m) = "[M] " <> m
+  entityChar = const $ "X" & style .~ markerStyle
+  entityCollision = const Nothing
+
+instance Draw Marker where
+  draw = const . raw $ Vty.char markerStyle 'X'
+  drawPriority = const maxBound
+
+markerStyle :: Vty.Attr
+markerStyle = Vty.defAttr
+  `Vty.withForeColor` Vty.red
+  `Vty.withBackColor` Vty.black