giscanner: remove C xml attribute formatter

Measuring the time it takes to build Gtk-3.0.gir
using a) the C version and b) the Python version
reveals there is no measurable difference to speak
of:

With C collect_attributes:
==========================

real	0m30.614s
real	0m32.255s
real	0m31.034s

With Python collect_attributes:
===============================

real	0m31.530s
real	0m31.549s
real	0m31.673s

Note that running g-ir-scanner under Python's
cProfile module does produce the 15 to 20%
difference mentioned in commit 98791e4955ea3955fec9c020bdfd3eee771ed241,
which is fully expected as cProfile does not
intrument the C version of the code but does
intrument the Python version, demonstrating
why one should not compare apples to oranges
when profiling  ;)
[WIP] 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] giscanner: include linemarkers in "gir/[gio|glib|gobject]-2.0.c"

Makes it obvious where a GTK-Doc comment block was picked up.

Note that these are not C pre-processor style linemarkers on
purpose to prevent g-ir-scanner's SourceScanner() from tripping
up over the non-absolute paths in the generated
"gir/[gio|glib|gobject]-2.0.c" files.
[wip]: gir xml schema

reset && time find /home/dieterv/gnome.org/checkout/gobject-introspection/gir/ /home/dieterv/gnome.org/prefix/share/gir-1.0/  -name "*.gir" -exec xmllint --noout --nonet --schema /home/dieterv/gnome.org/checkout/gobject-introspection/giscanner/gir/gir.xsd '{}' \;
[WIP] docs: improve layout
!!! for testing only !!!