api: added flag BLOB_DISK_CTL_USR1
api: added new write* API
api: renamed eblob_read_nolock() to eblob_read_ll()
api: added flags parameter to eblob_read_ll()
api: added eblob_read_flags() API
api: basic protection for eblob_write_ll()
api: basic protection for eblob_read_ll()
api: simplified eblob_read_ll()
api: add new API to public interface
api: replaced hacky eblob_read_flags() with eblob_read_return()

Now we have two consistient functions: eblob_read_return() and
eblob_write_return() that return wc.
api: protect against misuse via zeroing out wc
blob: more checks to eblob_csum_ok()
api: retain USR1 flag on fill()
blob: reformatted _eblob_read_ll() log
blob: make eblob_write_commit_ll() static
l2hash: removed unused l2hash lock
rwlock: hash->root_lock is now rwlock
rwlock: bctl->index_blocks_lock is now rwlock
data-sort: kick-in only on initial load
misc: renamed EBLOB_ITERATE_READONLY -> EBLOB_ITERATE_FLAGS_READONLY