chore(base16): add Base16 color theme plugins for shell and vim

nvim/plugins/base16-vim.vim

@@ -0,0 +1,14 @@
+" Base16 for Vim
+Plug 'chriskempson/base16-vim'
+
+function ActivateColorscheme()
+  if filereadable(expand("~/.vimrc_background"))
+    let base16colorspace=256
+    source ~/.vimrc_background
+  endif
+endfunction
+
+augroup ActivateColorscheme
+  autocmd!
+  autocmd User PlugLoaded call ActivateColorscheme()
+augroup END