add support of getdents64 to read directory entries (#519)

* add support of getdents64 to read directory entries

- remove readdir support
- add comment to describe file attributes
- This PR depends on hermit-os/kernel#1013

* add latest version of libhermit

* add test to open a file from the proc filesystem

/etc is not longer mounted and should not be used for a test

* rename some data structures to improve the backward compatability

* minor changes to pass the format check

* add test to read the directory entries

* using hexadecimal numbers instead decimal numbers

- improves the readability

* update kernel module