Implement user's config as init file and add directory into package.path

Create the user's config init file if lite user's config directory does
not exists.

No longer use the awkward package.searchers but instead add user's
config dir at the end of package path.

data/core/init.lua

@@ -86,6 +86,61 @@ local function project_scan_thread()
 end
 
 
+-- create a directory using mkdir but may need to create the parent
+-- directories as well.
+local function create_user_directory()
+  local dirname_create = USERDIR
+  local basedir
+  local subdirs = {}
+  while dirname_create and dirname_create ~= "" do
+    local success_mkdir = system.mkdir(dirname_create)
+    if success_mkdir then break end
+    dirname_create, basedir = dirname_create:match("(.*)[/\\](.+)$")
+    if basedir then
+      subdirs[#subdirs + 1] = basedir
+    end
+  end
+  for _, dirname in ipairs(subdirs) do
+    dirname_create = dirname_create .. '/' .. dirname
+    local success_mkdir = system.mkdir(dirname_create)
+    if not success_mkdir then error("cannot create directory: \"" .. dirname_create .. "\"") end
+  end
+end
+
+
+local function write_user_init_file(init_filename)
+  local init_file = io.open(init_filename, "w")
+  if not init_file then error("cannot create file: \"" .. init_filename .. "\"") end
+  init_file:write([[
+-- put user settings here
+-- this module will be loaded after everything else when the application starts
+
+local keymap = require "core.keymap"
+local config = require "core.config"
+local style = require "core.style"
+
+-- light theme:
+-- require "colors.summer"
+
+-- key binding:
+-- keymap.add { ["ctrl+escape"] = "core:quit" }
+]])
+  init_file:close()
+end
+
+
+
+local function load_user_directory()
+  local init_filename = USERDIR .. "/init.lua"
+  local info = system.get_file_info(USERDIR)
+  if not info then
+    create_user_directory()
+    write_user_init_file(init_filename)
+  end
+  return dofile(init_filename)
+end
+
+
 function core.init()
   command = require "core.command"
   keymap = require "core.keymap"
@@ -126,7 +181,7 @@ function core.init()
   core.add_thread(project_scan_thread)
   command.add_defaults()
   local got_plugin_error = not core.load_plugins()
-  local got_user_error = not core.try(require, "user")
+  local got_user_error = not core.try(load_user_directory)
   local got_project_error = not core.load_project_module()
 
   for _, filename in ipairs(files) do