[sd-utils] Drop sync from mount options.

We can safely drop sync from mount options since it significantly decreases the performance
of writing in addition to affecting the lifetime of SD cards.

Applications should take care to call sync()/fsync() after writing files.
[sd-utils] Refine mount options

Add dirsync,flush,noatime,discard,users to all filesystems.
Also add utf8 to vfat and ntfs filesystems in addition to the above mentioned
[sd-utils] adjust mount options for various filesystems
[sd-utils] Added a comment about NTFS not being tested
Merge pull request #11 from foolab/master

[sd-utils] Drop sync from mount options.