feat(fatfs): implement opendir & readdir

Signed-off-by: Rahix <rahix@rahix.de>

swym authored 5 years ago and rahix committed 5 years ago

This commit adds 3 new API calls

- epic_file_opendir()
- epic_file_readdir()
- epic_file_unlink()

and 2 new functions in Pycardium

- os.listdir()
- os.unlink()