feat: add an option for a function to ignore files (#223)

* refactor: use vim.pesc instead of implementing

* feat: add optional func to ignore in registering

* test: add tests for ignore_register function

* docs: add note for `ignore_register` option

* docs: add note for use case of `ignore_patterns`

doc/telescope-frecency.txt

@@ -443,9 +443,31 @@ Default:
   for Windows: `{ [[*.git\*]], [[*\tmp\*]], "term://*" }`
 Type: `string`
 
-Patterns in this table control which files are indexed (and subsequently which
-you'll see in the finder results).
+Glob patterns in this table control which files are indexed (and subsequently
+which you'll see in the finder results).
 
+			      *telescope-frecency-configuration-ignore_register*
+ignore_register ~
+
+Default: `nil`
+Type: `fun(bufnr: integer): boolean`
+
+In opening buffers, it registers the filename and timestamps into DB to
+calculate frecency scores later. `ignore_register` can take a buffer number
+and you can control whether the file should be registered or not.
+
+For example, you can ignore |'nobuflisted'| buffers to register with this below.
+>lua
+    telescope.setup {
+      extensions = {
+	frecency = {
+	  ignore_register = function(bufnr)
+	    return not vim.bo[bufnr].buflisted
+	  end,
+	}
+      },
+    }
+<
 				      *telescope-frecency-configuration-matcher*
 matcher ~
 
@@ -592,6 +614,11 @@ workspace files. It tries in order until it works successfully.
 If you like another commands, set them to this option, like
 `workspace_scan_cmd = { "find", ".", "-type", "f" }`.
 
+NOTE: When the plugin uses “4. Native Lua code”, it uses
+|telescope-frecency-configuration-ignore_patterns| to ignore candidates from
+listed entries. With other ways, such as `rg` and `fd`, it does not use the option
+because of performance consideration.
+
 				   *telescope-frecency-configuration-workspaces*
 workspaces ~