Include building hugo docs as part of test.

If the building of the doc fails, tarvis will fail.  This will help with
pull requests.
Remove hugolib.HTML and hugolib.URL types

These types were not be rendered correctly by the html/template package.
Removing them gets the correct behavior.

Fixes #74
Date rendering unit tests in pages

Tests to ensure rendering dates in templates is working correctly.
Actually, I was running into invalid templates not giving warnings when
I was trying to render a date.
Code reorg, helpers.go has been decomposed.

It started with wanting to move templates in template bundles and the
rest followed.  I did my best to start grouping related functions
together, but there are some that I missed.  There is also the method
Urlize that seems to be a special function used in both worlds.  I'll
need to revisit this method.
Adding Planner
Add file reporting to planner
Add Translate to target

Translate handles Ugly Urls.
Move to target.Filesystem

Moving the ugly urls logic to the target.  There is still UglyUrl logic
in page for the permlink but this is dealing with the generate of urls.
Expand the ShowPlan functionality
Remove page module dependence on opening files

The site is responsible for reading files, page only operates on
buffers.
Introduce source.Filesystem

This provides an abstraction over how files are processed by Hugo.  This
allows for alternatives like CMS systems or Dropbox, etc.
Homepage "/" respects PublishDir

It wasn't taking the value of PublishDir into consideration for the
special case of the homepage "/".

Fixes #75