Rename block_ruler to block_thematic_break (fix)

It was silently renamed in this megacommit:
https://github.com/asciidoctor/asciidoctor/commit/d98c8e9cd5e5793fdab6da7a0a6f37eb8349878b
Merge pull request #103 from jirutka/patch-15

Rename block_ruler to block_thematic_break (fix)
Merge pull request #94 from jirutka/patch-8

Fix html5/block_toc – add title id named after toc id
Merge pull request #95 from jirutka/patch-9

Fix html5/block_admonition – icons should have class “fa icon-”
Merge pull request #96 from jirutka/patch-10

Fix html5 math/stem
Merge pull request #98 from jirutka/patch-12

Fix html5/document – cleanup header and add some meta tags
Merge pull request #100 from jirutka/patch-14

Fix html5/inline_quoted – add missing type “mark”
Merge pull request #99 from jirutka/patch-13

Fix html5/block_listing – don't resolve fallback lang from :language
Merge pull request #97 from jirutka/patch-11

Fix html5/inline_anchor – add id and title for other types
Update doctest to 1.0.0.rc.3
Refactor slim/html5 templates
Add slim/html5/block_outline template
Fix html5/block_table - use stylesheet to set default table width

Reflects https://github.com/asciidoctor/asciidoctor/commit/d2537aacb6834bedf58ff6f5db4bd88afd67ce79
Add support for YouTube playlists to html5/block_video
Add support for video start/end anchor to html5/block_video
Update examples/html5/inline_quoted