sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

sys: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

- Increase dynamic range of filter coefficients from 28bit to 30bit.
This cause dramatic effect in overall precision and conversion quality
by pushing down most aliasing artifacts around -180 dB.

Spectrogram analysis/comparison:

http://people.freebsd.org/~ariff/z_comparison/z_28vs30/

- Guard against possible 64bit overflow during accumulation process by
slightly normalize and saturate sample and coefficient multiplication,
possible during extreme 32bit downsampling (eg. 380KHz -> 8KHz) with
custom preset that require more than ~7000 taps filter (which is
overkill).

- Add knobs through FEEDER_RATE_PRESETS to set dynamic range of filter
coefficients/accumulator and prefered polynomial interpolator:

COEFFICIENT_BIT:X
(where 1 <= X <= 30, default: 30)

ACCUMULATOR_BIT:X
(where 32 <= X <=64, default: 58)

INTERPOLATOR:I
(where I = ZOH, LINEAR, QUADRATIC, HERMITE, BSPLINE,
OPT32X, OPT16X, OPT8X, OPT4X, OPT2X)

Approved by: re (kib)

Slightly increase amount of bandwidth of resampling filter for
feeder_rate_quality=3. This have the benefit of reducing aliasing
artifacts due to alias masking.

Spectrogram analysis:

o Old preset (100:36:0.90)
http://people.freebsd.org/~ariff/z_comparison/z_q3_old.png

o New preset (100:36:0.92):
http://people.freebsd.org/~ariff/z_comparison/z_q3_new.png

Approved by: re (kib)

- Add a way to change filter oversampling factor through
FEEDER_RATE_PRESET "OVERSAMPLING_FACTOR:X .. .." where
X = log2(oversampling factor).

- Lower down default filter oversampling factor from 128
(log2 = 7) to 32 (log2 = 5), saving worth of 80 Kb.
The use of better polynomial interpolator will raise
its conversion quality/accuracy to match (or slightly
better) with previous settings.

- Bump driver version.

Move all sound related scripts to its own 'sound' subdir.

Suggested by: jmallett