Fixed size blocks refactor + chown support

[NorSomething]

Fixed size blocks refactor + chown support #26 #29

Context

The file system now uses block-based allocation (4 KBs each) strategy instead of a contiguous byte slice.
The file system now also supports chown support with UIDs and GIDs.

Description

The write, read and setattr functions of file.go have been modified to enable use of block-based allocations.
The attributes of both the file and the dir struct have been modified to have UID and GID fields in them enable ownership features in them.
fuse.AllowOther() has been added to main.go's mount code so felicitate chown support.

Tests

CRUD is tested to be working as intended.
chown test:

chown working as intended - only sudo users have the permission to change ownership.

Additional info

To have functioning chown support, I added fuse.AllowOther(), this allows any user to access the mount point. With this, anyone can change ownership. This issue is now handled by this validation code in dir.go's setattr :

if req.Header.Uid != 0 && req.Uid != req.Header.Uid {
    return syscall.EPERM
}

Here uid=0 is root. So if the user isn'tt root and is trying to chown something that is not in its UID then we throw permission error, otherwise we allow the change in ownership.

Important

As mentioned fuse.AllowOther() is being used here., but by default fuse will not recognize this and throw an error. To fix this, the user has to edit ~/etc/fuse.conf with elevated permissions and un-comment the line user_allow_other.

[Delta18-Git]

I think these changes make more sense, pending further discussion with @NorSomething and @Prana-vvb

Merging blocked due to conflict hell

[Delta18-Git]

Approved pending merge conflict resolution; might be best to push merging to after ART merge