binlog: Added stubs for binlog.

Start with basics: copy all data modifications to log and add ability to
apply logs onto blobs.
binlog: Implemented binlog initialization.

Added support for space preallocateion for platforms that have
posix_fallocate.
binlog: use strndup instead of malloc+strncpy
binlog: sorted includes
binlog: added simple logging.

For now it's based on eblob_log.
binlog: style fixes and error procesing
binlog: added header pointer to struct eblob_binlog_cfg
binlog: added sync subroutines
binlog: write binlog header on create
binlog: factor out binlog_hdr_write()
binlog: written initial binlog_hdr_read()
binlog: do not leak fd in case of an errors
binlog: augument logging messages

Admins probabli be happy.
binlog: added binlog header verification

Binlog is a very delicate thing - we can't blindly apply it to data, so
verification is essential.
binlog: sync after header write
binlog: prettyfication
binlog: added binlog_close and binlog_destroy
cmake: added posix_fadvise test
lib: blob: added eblob_pagecache_hint()
binlog: use eblob_pagecache_hint in binlog_close()