build: Replace INCLUDES with AM_CPPFLAGS

INCLUDES is deprecated and should not be used in modern autotools.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Fix the expansion of the REST_TYPE_PARAM macro

And this, kids, is why patches ought to be reviewed.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Fix annotations

Syntax matters.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Turn on introspection scanner warnings

So we have a fighting chance to actually fix them, instead of sweeping
them under the rug.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Update the ignore file

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Further annotation fixes

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Rename rest-docs from SGML to XML

It's an XML file, let's use the right extension.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
Add indices and annotation glossary

The latter, especially, avoids gtk-doc complaining about introspection
annotations in the documentation comments.

https://bugzilla.gnome.org/show_bug.cgi?id=712747
docs: Add missing gtk-doc annotations

https://bugzilla.gnome.org/show_bug.cgi?id=712747
docs: Add annotations to RestProxyAuth pausing methods

Both pause() and unpause() are referenced elsewhere in the API
reference, but have no formal documentation annotations.

https://bugzilla.gnome.org/show_bug.cgi?id=712747