simple.c: drop trailing whitespace
Use kill_block_super() in simplefs_kill_superblock()
Add FS_REQUIRES_DEV to fs_flags
Release bh in simplefs_fill_super()
Drop explicit cast sb_bread() return value to buffer_head

Since sb_bread() already have such a return value.
Add shell script to do some simple operations with simplefs

- create fs
- create files in it
- create dirs in it
- read files in it
- write files in it