gcsfuse v0.10.0

• Added support for setting arbitrary mtimes for files. Major changes:
• utimes(2) and friends no longer return ENOSYS.
• atime is ignored, and silently fails to take.
• mtime is stored in object metadata keyed by gcsfuse_mtime.
• Increased stat performance on Linux by a factor of 280x by allowing the
  kernel to cache inode attributes when -sstat-cache-ttl is set.
• Enabled writeback caching on Linux, increasing write performance by up to
  40x for small writes, and by a few times for large writes.