Raghumani/alloc inode impl

[raghumanimehta]

• Changed the type of inodes and blocks array to Box<[T]> because a static array couldn't handle the size on the stack. I also tried Box<[N; T]> through Box::new() however this first allocates the array on the stack and copies the array to the heap. I believe using Box<[T]> is fine since this is fixed size (determined at runtime though) and we do the checks using the constants.
• Added the implementation of allocating inodes.
• Added the implementation of freeing inodes
• Verified using unit tests.