Add :PreProcIfWrap command and C/C++ mappings

Quickly wrap a line or range in `#if 0`/`#endif` to quickly disable
compilation of sections of code.

plugin/commands.lua

@@ -126,3 +126,13 @@ vim.api.nvim_create_user_command('Rg', function(opts)
   end
   require('telescope.builtin').grep_string(grep_opts)
 end, { bang = true, nargs = '*' })
+
+vim.api.nvim_create_user_command('PreProcIfWrap', function(opts)
+  local buffer = vim.api.nvim_get_current_buf()
+  vim.api.nvim_buf_set_lines(
+    buffer, opts.line2, opts.line2, true, { '#endif' })
+  vim.api.nvim_buf_set_lines(
+    buffer, opts.line1 - 1, opts.line1 - 1, true, { '#if 0' })
+  local window = vim.api.nvim_get_current_win()
+  vim.api.nvim_win_set_cursor(window, { opts.line1, 5 })
+end, { range = true })