Merge pull request #9 from octabrain/master

Directory removal
added super_free_data_block_num and super_free_inode_num functions
added bitmap.h and bitmap.c
added bitmap.h and bitmap.c
moved bitmap functions to bitmap.c
implemented mkdir function
Flush the block to disk after removing directory entry

Signed-off-by: Prashant Shah <pshah.mumbai@gmail.com>