flac.md: fix "-q" misinformation, and more.

[H2Swine]

Hope I haven't messed up how pulls work. Wouldn't be the first time.

This intends to fix xiph#816 , the man page wrongly states -q 16 is permitted.

I have worked on more on the man page, but I don't want to put in too much in one request.

• Also, reworded -p for consistency with -q; -m and -M for clarity; and --lax for brevity.
• The following should have been done in the previous round: the --help text has the tagging options right after --picture. Did so here too.
• But, and this should either also be fixed in the help text or be rejected: --no-utf-8 is a tagging option - aren't those encoding-only? Moved and reworded, but reject as appropriate.

[H2Swine]

Looks like max thread count was wrong as well. Also reworded, clarifying that default is single-thread.

[H2Swine]

@ktmf01 : You had a few comments on the previous draft, I worked my way up to include the Examples subsection too, yes I introduced some errors there, now rectified. And I did some choice you might not approve upon (like emphasis on error and warning, and more subsectioning), which may be reverted before I run a PR.

• https://github.com/H2Swine/flac/commit/1639bed3af3eacd18db5d6429ff8268398297e7d with comments (but skipping those changes you had already given feedback on)
• Then it turned out a couple of glitches, so ... https://github.com/H2Swine/flac/commit/1639bed3af3eacd18db5d6429ff8268398297e7d#r161547748 links to a fix.

If/when this is ready for a PR ...

[H2Swine]

Time to try to finish it. A comprehensive rewrite, where the first part now looks more like xz man page style - whether that is an improvement is anyone's say I guess, but the information content was overdue for an overhaul.

https://github.com/H2Swine/flac/commit/a555fe1dd771027fba6c9ba34ad4fb129c54914d#r163204042 comments on those changes that are new since https://github.com/H2Swine/flac/commit/1639bed3af3eacd18db5d6429ff8268398297e7d . There are still a couple of questions up on changes that could have been taken on board.

Again: if/when this is ready for a PR ... now it is so much that I guess, not only "if/when @ktmf01 has the time to review whether a PR based on that first part is even a good idea", but also what details are still valid when 1.5.1 is shaping up. (Example: the document does say that as of 1.5.0, treatment of the ".aifc" file extension is inconsistent, and maybe that part of is obsoleted by 1.5.1.)

Edit: Now also with main.c updated to reflect the changes and fixes: https://github.com/xiph/flac/commit/51b21f7530ee65af3cfdc239838e0ef9c1904863#r163615829 . Of course I overlooked a couple of mistakes when doing that, so that comment links to an update.

[ktmf01]

I have completely lost track of what you're doing, mixing up too many things. Please just file a PR already, because I keep forgetting where to find your changes.

And if possible, please split uncorrelated stuff up. Maybe first fix things, then after we merge that, do some reordering. Or the other way around.