Patch for gnomemm-website

[Tao Wang <dancefire gmail com>]

Hi,

I found there are 2 more languages translated for the gtkmm website, however, they are not on the website.

After checkout  gnomemm-website, I found it looks like the Makefile.am is not working correctly, such as only generate html pages for 'de', rather than other languages. And I also realize adding a new language is not as easy as I thought.

So, I modified docs/Makefile.am to fix the bug and made the code more generic. Now, it only need to modify DOC_LINGUAS to add a new language to Makefile.am.

I also add 'Español' to the language list as alphabet order.

If it still not generate files for some languages, please 'make maintainer-clean', then './autogen.sh && make' again. It should be fine now.

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Regards

Tao Wang