libmu_cpp hacking

Today I added the FilterStream class that derives from the Stream and provides filtering mechanism, i.e. quoted-printable, base64, etc. Now I am able to run the exemplary iconv.cc. Moreover, I extended the Stream class and successfully ran new murun.cc.

I think the project work is slowly going in the right direction, but there is still a lot of work to be done. I definitely must put more effort into this. I wish I had more free time...