insert dummy <span> element with double-width space in tree toc
when <li> element has only child <ol> element. Closes #285.
aftermatter should have an appendix number by default. You can change this behavior by setting post_secnolevel parameter or adding [nonum] into the headline.
let content has chaptype to handle part better in tree TOC.
modify headline levels of pre/post in tree toc.
Merge branch 'master' into appendixstyle
null check.