template.html.txt add toc support (#207)
template.html.txt add toc support (#207)

- float TOC div in  top-right corner
- show h1,h2,h3 of content in TOC
- sync scroll and highlight curent in-view item in TOC
- click item in TOC to scroll to content position
- append 'EOF' marker and space to content, make sure last header can be
scroll to 0px
- 't' key to hide/show TOC ( need preview window has focus )
mike-ward/Markdown-Edit,punker76/Markdown-Edit