configure images to preview properly on GitHub

- set imagesdir per document
- remove hardcoded path to images in image macros
- override imagesdir in convert script
- use proper inline image syntax
- update convert script to accept list of formats
- set doctype to book in document
make use of kbd macro; set shared opts in convert script

- also correctly label OSX (Mac is not the proper term)
make use of additional UI macros
demo how to use open block to simplify complex lists

- additionally, put title above image instead of as attribute
enable syntax highlighting w/ coderay
fix list item in walkthrough
Merge pull request #11 from mojavelinux/image-paths-and-enhancements

Numerous configuration and syntax enhancements