added sample posts for post display testing

Populated _posts/ directory with six samples posts so that the post-related
pages and configurations can be tested. Will modify with all common HTML tags
to test styling in the future.
condensed includes into fewer files

Only two includes are actually needed: the navigation (used in multiple areas)
and a single wrapper around all content, which has the header and footer
within.
added blog layout and index page

Added a separate layout for the blog page that provides a custom_title
variable passed to the wrapper.html include, so that the title displays more
details about the paginated posts on display.
add blank static files for upcoming pages
use small-caps property for header navigation links