giscanner: only parse GTK-Doc comment blocks, ignore the rest

For example, GTK+ has over 15.000 comment blocks (/* ... */)
of which only about 5.000 are GTK-Doc comment blocks (/** ... */).

No need to store and parse those +-10.000 comment blocks
just to find out we don't care about them anyway.
docs: document some annotationparser.py hacking hints
giscanner: deprecate top level g-i specific GTK-Doc tags.

Rationale
---------

The first wave of improvements on AnnotationParser intended
to fix bug http://bugzilla.gnome.org/show_bug.cgi?id=672254
(multiline descriptions on tags not working correctly, polluting
the comment block description instead) had an unforeseen side
effect reported in bug http://bugzilla.gnome.org/show_bug.cgi?id=674658.

Analyzing this problem we found that even though comment blocks
having g-i specific tags before the comment block description
are technically malformed, the old annotationparser code happily
accepted these without complaint. During this analysis, a secondary
bug report (http://bugzilla.gnome.org/show_bug.cgi?id=676133)
was filed with the GTK-Doc project because it was found that the
same malformed tags did not result in the expected html output.

After discussing this with the GTK-Doc maintainers, we learned
that our g-i specific top level tags should never have existed
in the first place. The prefered notation for annotations that
apply to the identifier should be written on the identifier line,
for example like what we already do with (skip).

As a result, this patch deprecates g-i specific top level tags and
implements them as annotations on the identifier instead and at
the same time adds support for malformed comment blocks still
using g-i specific top level tags.

This means that all annotated code "out there" will continue to work
just fine with this version of g-i, but when a developer decides to
fix deprecation warnings in his/her comment blocks, the dependency
on g-i needs to be raised to a version that contains at least this
patch.

Overview of changes
-------------------

1) giscanner/annotationparser.py and giscanner/maintransformer.py
   have been adjusted to deprecate g-i specific top level tags
   and now implement these in terms of annotations on the identifier.
   The Attributes: tag and it's replacement (attributes) annotation
   continue to be broken (regression introduced in commit
   182fdfec261f36fa095484352b9b834861036907), which will be
   addressed in a followup patch.

2) AnnotationParser().parse_options() has learned to correctly parse
   multiple closing parentheses, which is for example required for the
   new syntax in tests/scanner/annotationparser/gi/annotation_type.xml:
   * AnnotationObject:hash-table: (type GLib.HashTable(utf8,gint8))

3) comment blocks in tests/*.c and tests/*.h had to be adjusted as
   these tests are not allowed to emit warnings. As a result, these
   test cases now no longer use g-i specific top level tags but
   annotations on the identifier instead.

https://bugzilla.gnome.org/show_bug.cgi?id=688897
https://bugzilla.gnome.org/show_bug.cgi?id=676133
https://bugzilla.gnome.org/show_bug.cgi?id=674658
Add a tool fixing GTK-Doc comment blocks in .c and .h files

Just a standalone script for now, should probably eventually
go into g-ir-doctool or g-ir-annotation-tool...
[WIP] docs: improve layout
!!! for testing only !!!
remove ./configure summary

${enable_tests} was removed in f5631640751b5a998b3616db78dd5dcd9ee62126
so there's nothing left to report about...
fix "make distcheck"