Update attach_mappings to use new actions api (#249)

README.md

@@ -201,11 +201,14 @@ end
 ["<C-i>"] = test_action,
 
 -- If you want your function to run after another action you should define it as follows
-local test_action = actions._transform_action(function(prompt_bufnr)
-  print("This function ran after another action. Prompt_bufnr: " .. prompt_bufnr)
-  -- Enter your function logic here. You can take inspiration from lua/telescope/actions.lua
-end)
-["<C-i>"] = actions.goto_file_selection_split + test_action
+local transform_mod = require('telescope.actions.mt').transform_mod
+local test_action = transform_mod {
+  x = function()
+    print("This function ran after another action. Prompt_bufnr: " .. prompt_bufnr)
+    -- Enter your function logic here. You can take inspiration from lua/telescope/actions.lua
+  end,
+}
+["<C-i>"] = actions.goto_file_selection_split + test_action.x
 
 ```
 
@@ -215,10 +218,13 @@ A full example:
 local actions = require('telescope.actions')
 
 -- If you want your function to run after another action you should define it as follows
-local test_action = actions._transform_action(function(prompt_bufnr)
-  print("This function ran after another action. Prompt_bufnr: " .. prompt_bufnr)
-  -- Enter your function logic here. You can take inspiration from lua/telescope/actions.lua
-end)
+local transform_mod = require('telescope.actions.mt').transform_mod
+local test_action = transform_mod {
+  x = function()
+    print("This function ran after another action. Prompt_bufnr: " .. prompt_bufnr)
+    -- Enter your function logic here. You can take inspiration from lua/telescope/actions.lua
+  end,
+}
 
 require('telescope').setup {
   defaults = {
@@ -259,6 +265,43 @@ function my_custom_picker(results)
 end
 ```
 
+To override a action, you have to use `attach_mappings` like this (prefered method):
+
+```lua
+function my_custom_picker(results)
+  pickers.new(opts, {
+    prompt_title = 'Custom Picker',
+    finder = finders.new_table(results),
+    sorter = sorters.fuzzy_with_index_bias(),
+    attach_mappings = function(prompt_bufnr)
+      -- This will replace goto_file_selection_edit no mather on which key it is mapped by default
+      actions.goto_file_selection_edit:replace(function()
+        -- Code here
+      end)
+
+      -- You can also enhance an action with post and post action which will run before of after an action
+      actions.goto_file_selection_split:enhance {
+        pre = function()
+          -- Will run before actions.goto_file_selection_split
+        end,
+        post = function()
+          -- Will run after actions.goto_file_selection_split
+        end,
+      }
+
+      -- Or replace for all commands: edit, new, vnew and tab
+      actions._goto_file_selection:replace(function(_, cmd)
+        print(cmd) -- Will print edit, new, vnew or tab depending on your keystroke
+      end)
+
+      return true
+    end,
+  }):find()
+end
+```
+
+See `lua/telescope/builtin.lua` for examples on how to `attach_mappings` in the prefered way.
+
 Additionally, the prompt's filetype will be `TelescopePrompt`. You can customize the filetype as you would normally.
 
 ## Status (Unstable API)