glupy: Added fop entry point definitions and structure definitions

The following fops are now extendable with Python:
* open
* readv
* writev
* opendir
* readdir
* readdirp
* stat
* fstat
* statfs
* setxattr
* getxattr
* fsetxattr
* fgetxattr
* removexattr
* fremovexattr
* link
* unlink
* readlink
* symlink
* mkdir
* rmdir

Also added fd, inode and iatt structures.

Signed-off-by: Ram <rraja@redhat.com>