adding/fixing up week 8
ignore `rawdata-master` link and `loess.gif`

For people like me who like to clone the `rawdata` repository, it is
probably best to put a symbolic link in place of the directory
`rawdata-master` in `week2`. This as well as a permanent copy of
`loess.gif` in `week4` should be ignored by git.
clean up redundant code

Since `week6/justsvd_duplicate_content.txt` does not contain any
information that is not already present in `week6/svacombat.Rmd` it can
safely be removed. (It only confuses.)