Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

Fix some regressions with the zgrep(1) wrapper.

- Handle whitespace with long flags that take arguments:

echo 'foo bar' > test
zgrep --regexp='foo bar' test

- Do not hang reading from stdin with patterns in a file:

echo foobar > test
echo foo > pattern
zgrep -f pattern test
zgrep --file=pattern test

- Handle any flags after -e:

echo foobar > test
zgrep -e foo --ignore-case < test

These two are still outstanding problems:

- Does not handle flags that take an argument if there is no
whitespace:

zgrep -enfs /etc/rpc

- When more than one -e pattern used matching should occur for all
patterns (similar to multiple patterns supplied with -f file).
Instead only the last pattern is used for matching:

zgrep -e rex -e nfs /etc/rpc

(This problem is masked in the unpatched version by the "any
flags after -e" problem.)

Add tests for the above problems.

Update the mange and add references to gzip(1) and zstd(1) and also
document the remaining known problems.

PR: 247126
Approved by: markj
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D25613

Adjust formatting of grep and zgrep manual pages.

grep(1) changes:
- Pet mandoc & igor.
- Stylize the text more with macros when appropriate.
- Stylize equal signs in long options (e.g., "--color=auto") with
the "Cm" macro as suggested by mdoc(7).
- Add missing arguments to --exlude, --exclude-dir, --include and
--include-dir.
- Remove a duplicate entry for the --context flag.
- Use a list in the EXAMPLES sections to make it easier to tell
which paragraphs belong to which example.
- Cross reference zgrep(1).

zgrep(1) changes:
- Fix Nd.
- Split synopsis into paragraphs for readability.
- Cross reference bzip(1), grep(1) and xz(1).

Reviewed by: bcr
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D16779

Use a script wrapper for <compress>grep

Import the wrapper script from zstdgrep (written by wiz@netbsd.org)

Modify it to support more than just zstd (adding support for gzip,
lzma, xz and bzip2)

Write a simple manpage dedicated for it.

Only use that new wrapper both for gnu grep and bsd grep

Next step will be removing code related to compression format from bsdgrep

Reviewed by: kevans
Approved by: kevans
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D15193