qdoc: Generate \keyword anchors at the top of the page

Currently, qdoc processes \keyword and \target the same way. The
negative effect of this is that when either command appears at the top
of a qdoc comment, the anchor it generates in the html file is just
above the details section on the html page. This is usually wrong,
especially for \keyword commands, where the anchor generated should
always be at the top of the page/text where the \keyword appears. This
update implements that. \target anchors are meant to be used when the
anchor should appear somewhere in the middle of the page/text, exactly
where the \target command appears.

Change-Id: Ibbbf1087562a977ff74ccd98febfe9310ecba8f0
Task-number: QTBUG-42290
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
qdoc: no longer autolinks symbols that begin with "__"

qdoc no longer tries to autolink symbols that begin
with two underscores. There may be other cases where
qdoc should not try to autolink. They should be
handled in this same place.

Change-Id: I5a39ea2bb0edec2289b8a4b1a9af1f33534093a1
Task-number: QTBUG-42441
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
qdoc: Generate the links-to-broken-links page

The cross-module link report now contains an entry
for the links to broken links subpage. It is the
last entry in the links-to-links table on the QA
page.

Change-Id: I9e0b3ba5f2efe76055902467348db878dbed9991
Task-number: QTBUG-41850
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
qdoc: Remove CR from command parameters

Although it is not recommended, it is allowed to have a carriage
return in a qdoc command parameter that is enclosed in curly
braces. qdoc is supposed to use QString::simplified() to sanitize the
string so that all whitespace is replaced by a single ' '. But in at
least one case, this didn't work, and the carriage return was left in
the string, which caused qdoc to report that it couldn't find links
that have the carriage return in them. The problem has been fixed by
replacing the carriage return with a ' ' right when and where it is
detected.

Change-Id: I31c31f19a1e4150b2e27613ecbac260c46a7109b
Task-number: QTBUG-42449
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
qdoc: Include source file and line number of links

Each entry in the link-to-link tables and in the
broken-links table now includes the source file
path of the file where the link or broken link
appears and the line number in that file. The
line number often refers to where the comment
that contains the link begins, so sometimes
the link or broken link appears further down in
that comment.

Change-Id: I692bfc173c8711bf26c9c59ad9771930c27e24a8
Task-number: QTBUG-41850
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>