Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r231871

Switch the license boilerplates to our standard one.

Advantages:
- Reduces the number of different license versions in the tree
- Eliminates a typo
- Removes some incorrect author attributions due to c/p
- Removes c/p error potential for future pmc manpages

Approved by: jkoshy, gnn, rpaulo, fabient (copyright holders)

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Use our canonical .Dd format.

Submitted by: Ulrich Spoerlein

Move the following functions into their own manual pages:
- pmc_attach(), pmc_detach().
- pmc_capabilities(), pmc_cpuinfo(), pmc_ncpu(), pmc_npmc(), pmc_pmcinfo(),
pmc_width().
- pmc_get_driver_stats().
- pmc_get_msr().
- pmc_read(), pmc_rw(), pmc_write().
- pmc_set().
- pmc_start(), pmc_stop().