====== volatile modules ======
Use ''dofile'' with file name to process file.

Using ''require'' makes module names independent from extension, but it creates
reference in ''package.loaded['module_name']'' table.
Reference is created after loading module, so reference can be destroyed only later,
by call <code lua>package.loaded['module_name'] = nil</code>

One method is to provide module constructor
<code lua>
local M = {}
function M.init()
  package.loaded['module_name'] = nil
  ...
end

return M
</code>