Implement AtkTableCell

https://bugzilla.gnome.org/show_bug.cgi?id=651353
doc: documentation for AtkTableCell, AtkTable, deprecations and padding

Index based methods forced ATK implementations to expose
the cells are direct children of the table. Something that
was complex in the practice. In fact some implementation
were not doing it, making the index-based methods not
properly implemented. This became even more clear with the
addition of AtkTableCell.

Additionally, this patch documents AtkTableCell and that
those cells should implement the newly added AtkTableCell
interface.
doc: move AtkRegistry section to the source file

So now is properly scanned by gtk-doc
doc: split API reference on categories
doc: add some forgotten symbols

atk-unused.txt now contains 6 symbols (from 14). Those 6 are not
relevant for documentation.
doc: add an overview

This is the same overview used for ATK releases. In any case
this should be improved and updated.
doc: more AtkTableCell documentation

* Adds when the symbols were added.
* Document the interface virtual methods.
doc: add new symbols section for 2.12 symbols
Release 2.11.90
Updated French translation
Updated Hungarian translation
atk/atk.symbols: Add Symbols for AtkTableCell

... so that they will also be exported in Windows builds
MSVC Builds: Update Introspection Build Process

GObject-Introspection was recently changed to support acquiring the name of
the DLL from a library (.lib, etc) that was passed into g-ir-scanner on
Windows, like the *nix builds, instead of directly passing in the name of
the DLL.  This updates the introspection build process, so that
introspection files for ATK can continue to be properly built.