sitegen += section links and xrefs
Review Request #1154 - Created Oct. 13, 2014 and submitted
.html files can have xmark anchors, like htmls anchor, except can be referenced from other pages.
xref is like href, but references xmarks
"pilcrow" section links: when mouse hovers over a heading, show a clickable link to that section. handy for when you want to answer a question w/a link to place in the docs.
fix to "breadcrumb" navigation: just show "ancestors", not also "older siblings"
excellent feedback is excellent. will merge soon
Revision 2 (+204 -30)