Improved rust, keybindings, org-mode export to HTML

Rust

- added ftplugin/after/rust.lua for rust keybindings

keybindings

- <space>[ and <space>] to goto prev and next diagnosticsw

Org mode

- added option for HTML export with pandoc

after/ftplugin/rust.lua

@@ -0,0 +1,10 @@
+local bufnr = vim.api.nvim_get_current_buf()
+
+vim.keymap.set(
+  "n",
+  "<space>E",
+  function()
+    vim.cmd.RustLsp({ 'explainError', 'current' })
+  end,
+  { silent = true, buffer = bufnr, desc = 'Rust: explain error at cursor' }
+)