Merge pull request #251 from krues8dr/master

Many changes: keyboard navigation, HTML, copy-to-clipboard, and more.
Merge pull request #252 from krues8dr/master

Added help key commands
Allow subsections that lack text

Per #113.
Clean up some comments
Only attempt to display subsection text if it exists

Per #113
Minor code formatting changes
Comment cleanup
Provide structural sibling data, and employ it as link rel tags

Per #119. This is still buggy, but 95% there.