Playing with git and racket.
Make log output prettier...fix some problems.
Move logging functions into logger.rkt.
Clean up git call. Convert checkout-site..
Make local-git and build-git controlled by git.rkt callers.
Turn log-level default back to zero.
Fix cleaning out the build directory...

...and don't nuke our git directory!
Begin converting build-site to racket.
Create slugify.rkt.
Initial work on converting site.py into site.rkt.

Page and Chapter classes converted and source directory scanning
for those pages and chapters.
Add call to (generate-site) to build-site.
Implement copy-static-files
Clean up chapter->page generation.

It didn't belong inside of the Chapter class, so pull it into its
own function. Also, the recursive construct was less clear than
iterating using for/list. Finally, we aren't generating a ton of
pages, so don't pre-optimize the regular expressions at the expense
of readability.
Basic chapter/page generation

Still need to be able to create thumbnails and copy cover images.
Add images.rkt and (make-thumbnail).
Use (make-thumbnail) to generate page thumbnails.
Copy covers and generate cover thumbnails.
Add render.rkt for rendering mustache templates.
Create mustache templates for page and chapter.
Render templates for pages and chapters.