hier(7): improvement, modernisation

Consistent use of lowercase, spacing between sections, etc.

Cease mentioning floppy disks.

De-list /usr/share/misc/fonts/, which has been ??? (without a
description) for twenty-seven years.

Change zpool to pool. (zpool is a command.)

Uppercase PPP for Point-to-Point Protocol.

A few other changes to wording, including avoidance of the phrase
pre-fab.

Update the descriptions of:

• /tmp/
• /usr/share/misc/
• /var/preserve/
• /var/tmp/
• /var/tmp/vi.recover/.

Refer to vi(1) instead of ex(1).

https://bugs.freebsd.org/261349

PR: 261349
Reviewed by: mhorne
Approved by: mhorne
Pull request: https://github.com/freebsd/freebsd-src/pull/763