Highlight mtab files with fstab highlighting

[kidonng]

This is mentioned in #696 (comment), but somehow not implemented.

[sharkdp]

Thank you very much for your contribution!

I wasn't sure if it really was the same syntax. Do you have any information on that?

[kidonng]

Quoting: https://github.com/karelzak/util-linux/blob/fb9ed3b409c05752a06619b2a5f02f5a21b3bb62/sys-utils/mount.8.adoc#the-files-etcfstab-etcmtab-and-procmounts:

The programs mount and umount(8) traditionally maintained a list of currently mounted filesystems in the file /etc/mtab.

The difference is basically that fstab is managed by the user and mtab by the system. The syntax should be the same.

[sharkdp]

Thank you!