Added an option to use base36 for slugs

- Switched to "slug" module for title slugs
- Use "bases" module for generating base36 slugs
  - base36 slug uses post timestamp in seconds
- Added slugType = ( "title" | "base36" ) config param
Merge pull request #5 from gschier/slugRefactor

Added an option to use base36 for slugs. Addresses #4