More flexible output indentation

Increment the indentation _before_ printing anything, so that we can
uniformly indent (and soon outdent!) both describes and its.
Add generic end function to denote end of 'blocks'

* Allows us to end both describe and it sections.
* Keeps the old end_describe for backwards compatibility
* Adds an old-style shpec file to test backwards compatibility
Add deprecation warning for end_describe
Update the documentation with new block syntax
Merge pull request #43 from rylnd/end

Add proper 'end' function