feat(version-control): add module for git-gutter as an alternative to diff-hl

For now I'm still using diff-hl, but I wanted to get git-gutter
configured so I can easily give try it out and compare it against
diff-hl.

modules/version-control/siren-git-gutter.el

@@ -0,0 +1,33 @@
+;;; siren-git-gutter.el --- jimeh's Emacs Siren: git-gutter configuration.
+
+;;; Commentary:
+
+;; Basic configuration for git-gutter.
+
+;;; Code:
+
+(use-package git-gutter
+    :hook
+    (prog-mode . git-gutter-mode)
+    (text-mode . git-gutter-mode)
+
+    :custom
+    (git-gutter:update-interval 1)
+    (git-gutter:added-sign "+")
+    (git-gutter:modified-sign "=")
+    (git-gutter:deleted-sign "-"))
+
+(use-package git-gutter-fringe
+  :if window-system
+  :after git-gutter
+  :config
+  ;; Customize fringe bitmaps
+  (define-fringe-bitmap 'git-gutter-fr:added
+    [#b00000011] nil nil '(center repeated))
+  (define-fringe-bitmap 'git-gutter-fr:modified
+    [#b00000011] nil nil '(center repeated))
+  (define-fringe-bitmap 'git-gutter-fr:deleted
+    [#b00000011] nil nil '(center repeated)))
+
+(provide 'siren-git-gutter)
+;;; siren-git-gutter.el ends here