v0.1.3

• Fix parse two markdown document use same MarkdownPipelineBuilder , one document without [toc] and the other one has, the generated toc block will contains both. This bug is occur case I use the TocOptions.Headings to store the headings, and don't clear them when all renderer completed, not just clear after toc rendered.
• After fixed, markdown document can has more than one [toc] , and all of these can be rendered, though it's useless.