tweak layout in readme installation markup

merge upgrade of highlight.js, add base styles to pre code, dont limit language detection in index.html #809

Some code blocks weren't indented, so they ended up messing up the numbering. Indenting them fixed it.

small fix for issue #814

fixed two minor bugs, a twohanded gesture may not have a direction, and if autoCenter is of, the tipPosition was in the wrong scope

renamed markdown attributes for clarity and consistency: data-vertical -> data-separator-vertical, data-notes -> data-separator-notes