docs: Fix a typo in the README
tests: Remove unnecessary non-NULL test

It was confusing Coverity.

Coverity issue: #74584
core: Add padding members to class structures

This gives us flexibility for soft ABI breaks in future if needed, after
we lock down the ABI entirely.
core: Mark all API as stable and impose API and ABI stability guarantees

It’s time for libgdata to grow up and start guaranteeing some stability
for its users. In this vein, it’s already been API stable for around 3
years (since 0.9.1) — it’s about time that was made explicit.

http://upstream-tracker.org/versions/libgdata.html is quite interesting.
Add --disable-tests to skip the building of tests

https://bugzilla.gnome.org/show_bug.cgi?id=739395
core: Eliminate ISO 8601 formatting workaround for dates

Google have fixed the issue upstream, so the workaround is no longer
needed. Thanks Google!

https://bugzilla.gnome.org/show_bug.cgi?id=737799
https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3595
tests: Remove pointless async authorizer tests from contacts.c

The authorisers are tested separately, and don’t need to be re-tested in
each unit test suite.
tests: Update Contacts test traces for ISO 8601 date changes

https://bugzilla.gnome.org/show_bug.cgi?id=737799
tests: Temporarily disable some Contacts test assertions

Seems these elements broke on the server at some point.

https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3662
Updated Turkish translation