Add a method to retrieve type to post, page and draft
add a class `FrontmatterDefaults` for handling of frontmatter defaults
make frontmatter defaults available to liquid
Retrieve frontmatter defaults when retrieved internally

This is for example possible for layout defaults to take effect.
Add basic cucumber features for frontmatter defaults
fix for Ruby 1.8
improve validation code
add inline code docs
Add site documentation for the new feature
improve path checking, now using Pathname instead of regex
fix minor docs quirk
move cucumber features to own file
fix slash handling for paths
more robust cucumber features
fix frontmatter defaults for custom paths

The Page#path or Post#path can be overriden by by a frontmatter
setting. This causes path-based frontmatter default detection to
fail. Add test to demonstrate this and fix it.
Merge branch 'master' into frontmatter-defaults
change cucumber feature to test for precedence too
adjust frontmatter defaults precedence handling

Before, the bottom-most default set had highest precedence. Instead,
now the set with a longer i.e. more specific path has precedence and
sets with a type setting have precedence over those without one. In
case of equal precedence the bottom-most still wins.
document frontmatter defaults precedence
oops, fix minor indentation quirk