I am using a slim_version of cowboy, I have also tried that on slim_yaws on nitrogen. What puzzles me is the abrupt deletion of the wf.hrl file by the VM. I do not understand what causes this!! Here is what appears in the console.
Warning. Deleted "wf.hrl" file included in existing src files: [list_module_files_with_the_wf.hrl_include >]
I am puzzled because the module which use the wf.hrl cannot compile after its deletion. I have experienced it on slim_cowboy and slim_yaws. It is abrupt!