index file for subdirectory support

[jonbullock]

(See jbake-org/jbake.org#26 for original issue)

Currently JBake supports index/home page for the whole project.

Some time user like to have a index page in each folder

Scenario

Assuming I create a website where homepage is not a blog and I like to have a separate index page inside my 'blogornews` folder or i may be like to have a folder with a new subproject support and have one index page.

Currently if i like to create a index file in sub directory i like to have one template in template folder and then have one index file in content folder with a name of index.xxx file with necessary header detail with empty content.

If we give some home index page support provided for home page to sub folders it will be easy way to have a new different template for sub project.