Fix local linking issues

[zkamvar]

This fixes a few issues with local links in some situations:

1. links originating from a page in the root of the repository now are treated
   the same way as links from within a folder in the repository (e.g.
   a link that is [first episode](episodes/introduction.md) will now properly
   link to the episode in the rendered HTML.
2. links to the setup page will now properly render to the correct place (index)
3. The setup will contain a section (eventually to be replaced by a
   callout with nav elements).

This also addresses #250 where the BASH was interpreting 08 as octal and freaking out.

This will fix #260 and #250