Added safeHtml template function
Normalize paths within hugo

filepath was used inconsistently throughout the hugolib.  With the
introduction of source and target modules, all path are normalized to
"/".  This simplifies the processing of paths.  It does mean that
contributors need to be aware of using path/filepath in any module other
than source or target is not recommended.  The current exception is
hugolib/config.go
Move alias rendering to target
Move alias logic to target module

I want to move all logic to writing aliases to target so I can pave the
way for writing aliases specific to other runtimes (like .htaccess for
apache or a script for updating AWS or symlinking on a filesystem).
Remove RenderedContent from page.

The output is written directly to disk after being written.  Not
entirely sure why it was split into two steps.
Add /index.html to unadorned alias paths

Bring code to be better in line with documentation.
Initialize HTMLRedirectAlias before ShowPlan()

Without it, no alias information is generated when running --check
Fix alias documentation.

Fixes #79