move config/plugins to plugins

same reason as the core config directory

config/plugins/seoul256.vim

@@ -1,7 +0,0 @@
-let g:seoul256_background       = 237
-let g:seoul256_light_background = 253
-
-colorscheme seoul256
-
-noremap <leader>sl :colorscheme seoul256-light<CR>
-noremap <leader>sd :colorscheme seoul256<CR>

plugins/seoul256.vim

@@ -0,0 +1,37 @@
+"  _____             _ ___ ___ ___      "
+" |   __|___ ___ _ _| |_  |  _|  _|     "
+" |__   | -_| . | | | |  _|_  | . |     "
+" |_____|___|___|___|_|___|___|___|.vim "
+"
+"   seoul256.vim is a low-contrast Vim color scheme based on Seoul Colors.
+"   Works on 256-color terminal or on GVim
+"   by Junegunn Choi (https://github.com/junegunn/seoul256.vim)
+"
+"   Theme           Range       Default
+"   -----           -----       -------
+"   seoul256        233 - 239   237
+"   seoul256-light  252 - 256   253
+
+let g:seoul256_background       = 237
+let g:seoul256_light_background = 253
+colorscheme seoul256
+
+function! ToggleColorscheme()
+    if g:colors_name == 'seoul256'
+        colorscheme seoul256-light
+    else
+        colorscheme seoul256
+    endif
+endfunction
+
+function! SetColorschemeDark(value)
+    let g:seoul256_background = a:value
+    colorscheme seoul256
+endfunction
+
+function! SetColorschemeLight(value)
+    let g:seoul256_light_background = a:value
+    colorscheme seoul256-light
+endfunction
+
+noremap <leader>st :call ToggleColorscheme()<CR>

plugins/youcompleteme.vim

@@ -1,4 +1,4 @@
-let g:ycm_global_ycm_extra_conf = $XDG_CONFIG_HOME . "/vim/config/youcompleteme/ycm_extra_conf.py"
+let g:ycm_global_ycm_extra_conf = g:vim_config_home . "/config/plugins/youcompleteme/ycm_extra_conf.py"
 let g:ycm_autoclose_preview_window_after_completion = 1
 let g:ycm_register_as_syntastic_checker = 1
 let g:ycm_server_keep_logfile = 1