Limit ourselves to Chinese

We declare ourselves as handling Chinese in the XML component file, and
(as far as I know) incredibly few people use Cangjie/Quick to input
Japanese.

So let's limit what we do a bit for now, and try to make it rock.

If people really want Japanese, we can add it later on.
Drop unimplemented options

We shouldn't show option to the user that has no effect.

When the time comes to reimplement them, this commit can just be
reverted.

fixes #13
Make sure IBus will detect the engine

By default, the Autotools install with prefix=/usr/local

That means our XML component goes into /usr/local/share/ibus/component

This is wrong, because then IBus only reads for XML files in its own
PKGDATADIR (at least that's what the IBus source code tells me).

This commit ensures that no matter what the install prefix is for
ibus-cangjie, our XML component file will be installed in IBus'
PKGDATADIR.

fixes #10