nvim: add toggleterm plugin

nvim/.config/nvim/lua/plugins/toggleterm.lua

@@ -0,0 +1,9 @@
+return {
+  'akinsho/toggleterm.nvim',
+  version = '*',
+  config = true,
+  keys = {
+    { '<F2>',  '<cmd>ToggleTerm size=25<CR>', mode = { 'n', 'i', 't', }, },
+    { '<C-w>', [[<C-\><C-n><C-w>]],           mode = 't' },
+  }
+}