feat!: rewrite TOhtml in lua

Co-authored-by: wookayin <wookayin@gmail.com>
Co-authored-by: clason <c.clason@uni-graz.at>
Co-authored-by: Lewis Russell <me@lewisr.dev>

runtime/plugin/tohtml.lua

@@ -0,0 +1,11 @@
+if vim.g.loaded_2html_plugin ~= nil then
+  return
+end
+vim.g.loaded_2html_plugin = true
+
+vim.api.nvim_create_user_command('TOhtml', function(args)
+  local outfile = args.args ~= '' and args.args or vim.fn.tempname() .. '.html'
+  local html = require('tohtml').tohtml()
+  vim.fn.writefile(html, outfile)
+  vim.cmd.split(outfile)
+end, { bar = true, nargs = '?' })