bugfix: rmdir must not remove regular file

See merge request zdvresearch_bsc/adafs!99

Remove the optional inode support

See merge request zdvresearch_bsc/adafs!98

Refactor adafs internal read/write funciton

See merge request zdvresearch_bsc/adafs!97

the functionality wasn't used at all and it will be implemented later
with a different approach

 - Added adafs_pwrite and adafs_pread functions:
        they accept an OpenFile pointer instead of a fd so that can be
        called by function that already accessed the OpenFileMap.

 - Moved the writev function into internal adafs functions.

 - Added internal adafs_write function:
        instead messing up with the file position at the interception
        layer, we can use this internal function that hides the update of the
        file position two.

various metadata related improvements

See merge request zdvresearch_bsc/adafs!96

Instead of passing only the mode as paramenter, we now pass an entire
Metadata object in such a way that the parameter can be configured at
compile time. For instace if we support symlinks we would like also to
pass the target path

Can be used to retrieve the Metadata object for a named path

In several places the adafs_stat function have been replaced with this
new adafs_metadata. This allowed to avoid the construnction of the
additional `struct stat`.

pos is already set to zero in the OpenFile constructor, thus there
is no need to do that also in the OpenDir constructor

fix buffer overflow: readlink write

See merge request zdvresearch_bsc/adafs!94

readlink write at most PATH_MAX, thus we need to support also the worst case
scenario in which all the bytes are written.

Bugfix: links to pipe raise exception

See merge request zdvresearch_bsc/adafs!95

In the kernel VFS some file descriptors under /proc/<PID>/fd/ could be
links to a pipe, this is a special case in which the `readlink` function
would not work. So when we detect this case we forward to kernel

Path resolution

Closes #56

See merge request zdvresearch_bsc/adafs!91

During resolution of `..` component the last slash position won't be updated.

number of matched component should be decremented only when
component that was counted as matched gets removed.

for instance when `/tmp/ext/..` gets resolved to `/tmp` we should not
decrement the matched counter cause we didn't match ext before.

when resolving path we don't want always
to resolve also the last components if it is a link. Cause in some cases
we want exactly the path of that link and not the one it points to.

lstat and readlink are some example of functions that don't want to
resolve the last link.

relativize path now accepts a file descriptor.

If fd is AT_FDCWD relative path need to be considered with respect to
the current working directory. Otherwise the path is relative to the
directory with the given file descriptor

when the resolved path is the root dir we were returning an empty string

when only PSP are given as input path '//////', we got segfault