Refactor: use a unified log function

core/autocommands.vim

@@ -42,8 +42,7 @@ augroup END
 " https://vi.stackexchange.com/a/20397/15292.
 augroup auto_read
   autocmd!
-  autocmd FileChangedShellPost * echohl WarningMsg
-        \ | echo "File changed on disk. Buffer reloaded!" | echohl None
+  autocmd FileChangedShellPost * call utils#Log("File changed on disk. Buffer reloaded!", 'warning')
   autocmd FocusGained,CursorHold * if getcmdwintype() == '' | checktime | endif
 augroup END
 

core/ui.vim

@@ -61,9 +61,7 @@ let s:colorscheme_func = printf('s:my_theme_dict.%s()', s:theme)
 if has_key(s:my_theme_dict, s:theme)
   execute 'call ' . s:colorscheme_func
 else
-  echohl WarningMsg
-  echomsg 'Invalid colorscheme function: ' s:colorscheme_func
-  echohl None
+  call utils#Log('Invalid colorscheme function: ' . s:colorscheme_func, 'error')
 endif
 "}}
 "}