Remove 'open_compat' module

[deathaxe]

This PR...

1. removes open_compat and file_not_found_error module which were required for compatibility with python 2 only.
2. use fobj as file object variable instead of f or arbitrary other characters.
3. pass encoding to open(..., encoding='utf-8') instead of manually handling that
4. Prefer json.load(fobj) over json.loads(fobj.read())
5. Create empty files in binary mode. No need to allocate an encoder for writing nothing.

[wbond]

Looks good to me, thanks for cleaning this up!