fix menubar to support directories

the affilated/index.html menubar was broken because it pointed to files
inside the affiliated directory - this fixes that.
added montage-wrapper as an affiliated package
Merge pull request #29 from eteq/add-montage-wrapper

add montage-wrapper as an affiliated package
Merge pull request #27 from eteq/fix-affiliated-menubar

fix affiliated.astropy.org menubar
added pydl to affiliated package registry