Support manual tagging of .Pp, .Bd, .D1, .Dl, .Bl, and .It.
In HTML output, improve the logic for writing inside permalinks:
skip them when there is no child content or when there is a risk
that the children might contain flow content.

Represent mdoc(7) .Pp (and .sp, and some SYNOPSIS and .Rs features)
by the <p> HTML element and use the html_fillmode() mechanism
for .Bd -unfilled, just like it was done for man(7) earlier, finally
getting rid both of the horrible <div class="Pp"></div> hack and
of the worst HTML syntax violations caused by nested displays.

Care is needed because in some situations, paragraphs have to remain
open across several subsequent macros, whereas in other situations,
they must get closed together with a block containing them.

Some implementation details include:
* Always close paragraphs before emitting HTML flow content.
* Let html_close_paragraph() also close <pre> for extra safety.
* Drop the old, now unused function print_paragraph().
* Minor adjustments in the top-level man(7) node formatter for symmetry.
* Bugfix: .Ss heads suspend no-fill mode, even though .Ss doesn't end it.
* Bugfix: give up on .Op semantic markup for now, see the comment.

Now that markdown output is tested for almost everything, test all
input files in -T markdown output mode by default and only mark
those files with SKIP_MARKDOWN that are not to be tested.
Much easier to read, and almost minus 40 lines of Makefile code.

enable -T markdown tests of filled displays and tagged lists

better handle empty .Bd .Bl .D1 .Dl blocks

after several improvements to -Tman went in,
enable lots of related regression tests

Represent mdoc(7) .Pp (and .sp, and some SYNOPSIS and .Rs features)
by the <p> HTML element and use the html_fillmode() mechanism
for .Bd -unfilled, just like it was done for man(7) earlier, finally
getting rid both of the horrible <div class="Pp"></div> hack and
of the worst HTML syntax violations caused by nested displays.

Care is needed because in some situations, paragraphs have to remain
open across several subsequent macros, whereas in other situations,
they must get closed together with a block containing them.

Some implementation details include:
* Always close paragraphs before emitting HTML flow content.
* Let html_close_paragraph() also close <pre> for extra safety.
* Drop the old, now unused function print_paragraph().
* Minor adjustments in the top-level man(7) node formatter for symmetry.
* Bugfix: .Ss heads suspend no-fill mode, even though .Ss doesn't end it.
* Bugfix: give up on .Op semantic markup for now, see the comment.

Now that markdown output is tested for almost everything, test all
input files in -T markdown output mode by default and only mark
those files with SKIP_MARKDOWN that are not to be tested.
Much easier to read, and almost minus 40 lines of Makefile code.

enable -T markdown tests of filled displays and tagged lists

better handle empty .Bd .Bl .D1 .Dl blocks

after several improvements to -Tman went in,
enable lots of related regression tests

Now that markdown output is tested for almost everything, test all
input files in -T markdown output mode by default and only mark
those files with SKIP_MARKDOWN that are not to be tested.
Much easier to read, and almost minus 40 lines of Makefile code.

enable -T markdown tests of filled displays and tagged lists

better handle empty .Bd .Bl .D1 .Dl blocks

after several improvements to -Tman went in,
enable lots of related regression tests