Return an error (other than 0) when ./hugo fails

Being a good OS citizen so folks can compose hugo into their tool chain.
Also helps with git bisect run.
Use s everywhere for consistency

Signed-off-by: Noah Campbell <noahcampbell@gmail.com>
Abstract html/template dependency

Signed-off-by: Noah Campbell <noahcampbell@gmail.com>
Add support for amber files

If a layout file ends with .amber it will interpreted as a Amber file

Signed-off-by: Noah Campbell <noahcampbell@gmail.com>
Include building hugo docs as part of test.

If the building of the doc fails, tarvis will fail.  This will help with
pull requests.