Move or remove misc files sitting in docs

- [x] https://github.com/enthought/chaco/blob/master/docs/CHANGES.txt (#710)
- [ ] https://github.com/enthought/chaco/blob/master/docs/chaco_layout.txt
- [x] https://github.com/enthought/chaco/blob/master/docs/datamodel_hierarchy.txt (appears to be old / redundant - see "Chaco Object Model" section of developer reference -Aaron) (#711)
- [ ] https://github.com/enthought/chaco/blob/master/docs/event_handling.txt (some of this is redundant info spread across current docs, but it might be good to have a fully dedicated Events section in the documentation? -Aaron)
- [x] https://github.com/enthought/chaco/blob/master/docs/introduction.txt (nothing new here really -Aaron) (#711)
- [x] https://github.com/enthought/chaco/blob/master/docs/scipy08_tutorial.keynote.tgz

We can probably extract meaningful information from these files - and we could potentially remove the Doc files and move the pdf files into an archive folder.

- [ ] https://github.com/enthought/chaco/blob/master/docs/Chaco_2_Design.doc and https://github.com/enthought/chaco/blob/master/docs/Chaco_2_Design.pdf
- [ ] https://github.com/enthought/chaco/blob/master/docs/datamodel.doc and https://github.com/enthought/chaco/blob/master/docs/datamodel.pdf