Updated plugins, minor cleanup, removed now deprecated FixCursorHold.…

…nvim plugin

Some more refactoring:

- dropped unused/no longer necessary plugins
  (nvim-notify, lightbulb, nui.nvim);
- replaced dressing with my custom, stripped
  down, Fennel version of it;
- replaced package info, with my bare bones
  Fennel version of it;
- broken the old "monolithic" setup into plugins:
  -- dropped the config/init.fnl proxy in favor of:
     1) requiring directly where needed or 2) including
     smaller libs where they are actually used;
  -- dropped misc.fnl and moved the code to where
     it was actually used (commands, plugins, etc.);
  -- signs moved to an after/plugin;
  -- start.fnl moved to plugin/init.fnl;
  -- go and fennel functionality moved in plugins
     of their own;
  -- trim commands moved to a plugin;
- removed no longer necessary hacks/settings:
  -- gomod is now auto-detected;
  -- tagsfunc and omnifunc are now set by default;
- gopls was updated to expose the latest features,
  even though nvim is not yet ready for them (inlay hints);
- added a script to benchmark startuptime.

Autocommands cleanup

Updated to keep up with changes; updated plugins

Addopted the new nvim_create_autocmd() & other cleanup

Switched to filetype.lua and vim.keymap, misc other cleanup

Further refining the use of new user commands API

Switched to the new nvim_add_user_command() for commands,

updated plugins, misc other cleanup (removed a couple of options that
are now on by default, etc.).

Minor cleanup

Using tflint as a LSP directly, dropped efm config for it; updated pl…

…ugins