add libmpg123-dev to debian package now that the fix for precise is in 0.3.6

also add rst2pdf even though the new pdf generation didn't make it to
0.3.6. On git master, it builds the pdf manual (in
/usr/share/doc/mpv.pdf.gz). On 0.3.6, its just a few more packages
that can be removed after build.

Closes #29
oops: fix location of some docs in debian pacakge
update README.Debian now that mpg123 is enabled