Feat: Sort Discussions by File Name (#102)

This MR adds the ability to sort discussions by file name, rather than just by date.

This is an optional configuration that can be passed in on startup. The MR also introduces a test suite for the Lua code that runs through Neovim, so that the plugin can be fully tested with required dependencies and APIs.

Major props to @johnybx for the hard work on this change!

README.md

@@ -57,6 +57,7 @@ return {
     "nvim-lua/plenary.nvim",
     "sindrets/diffview.nvim",
     "stevearc/dressing.nvim", -- Recommended but not required. Better UI for pickers.
+    "nvim-tree/nvim-web-devicons" -- Recommended but not required. Icons in discussion tree.
     enabled = true,
   },
   build = function () require("gitlab.server").build(true) end, -- Builds the Go binary
@@ -104,7 +105,6 @@ gitlab_url=https://my-personal-gitlab-instance.com/
 
 The plugin will look for the `.gitlab.nvim` file in the root of the current project by default. However, you may provide a custom path to the configuration file via the `config_path` option. This must be an absolute path to the directory that holds your `.gitlab.nvim` file.
 
-
 ## Configuring the Plugin
 
 Here is the default setup function. All of these values are optional, and if you call this function with no values the defaults will be used:
@@ -135,6 +135,7 @@ require("gitlab").setup({
     relative = "editor", -- Position of tree split relative to "editor" or "window"
     resolved = '✓', -- Symbol to show next to resolved discussions
     unresolved = '✖', -- Symbol to show next to unresolved discussions
+    tree_type = "simple", -- Type of discussion tree - "simple" means just list of discussions, "by_file_name" means file tree with discussions under file
   },
   info = { -- Show additional fields in the summary pane
     enabled = true,
@@ -195,10 +196,13 @@ require("gitlab").setup({
   },
   colors = {
     discussion_tree = {
-      username = 'Keyword', -- The highlight group used, for instance 'DiagnosticSignWarn'
-      date = 'Comment',
-      chevron = 'Comment',
-    }
+      username = "Keyword",
+      date = "Comment",
+      chevron = "DiffviewNonText",
+      directory = "Directory",
+      directory_icon = "DiffviewFolderSign",
+      file_name = "Normal",
+      }
   }
 })
 ```