Add Html5 Boilerplate, closes #6

Imported all files and adapted them to the build process. Some final
tweaking still needs to be done:

- Pick a specific version of H5bp (since I'm now mixing the master
  branch from their git repo, and the official download), and list the
  version number in the docs
- Adapt the 404 template (right now it isn't integrated in the
  templating system)
- Document any deviations from the boilerplate for clarity
Merge branch 'h5bp' into develop