Linksupdate

1. External links are partially (small part only) corrected. I'm going to work it out.
2. File coding corrected (small part) from dos to unix - that's why sometimes github's diff highlights all the lines of a file.
3. Absolute addressing to http://www.diveintopython.net/ removed and replaced by "/". Allows to run the html at other sites. It changed 128 files.
4. Backup files removed.
relative link