Fix orientation bugs

Maintain fontsize and and adapt width when switching to landscape mode.
Pass the filename as an argument to Document#slug
Add 'title' to url_placeholders
Test titles in document permalinks
Document the :title variable
Properly handle titles with trailing punctuation
Test documents without a title
Rename 'slug' to 'sluggify' and clean up code
Merge pull request #2862 from mischah/fix-orientation-bugs
Update history to reflect merge of #2862 [ci skip]
Add inspect filter
Merge pull request #2867 from chibicode/add-inspect-filter
Update history to reflect merge of #2867 [ci skip]
Move Document#sluggify to Utils#slugify
Replace the 'name' parameter with 'string'
Revise Utils#slugify with inspiration from Rails
Add tests for Utils#slugify
Support a new `relative_include` tag
Merge pull request #2864 from kansaichris/add-title-to-collection-urls
Update history to reflect merge of #2864 [ci skip]