v0.3.1 - highlight code in markdown + fix doc render bug

fixes and improvements motivated by the excellent work by @PhilippMDoerner in adding nimibook documentation to @can-lehmann's excellent GUI library owl kettle can-lehmann/owlkettle#34

What's Changed

• add highlight.js for markdown code blocks by @HugoGranstrom in #74
• Fix toc render bug, miss closing tags, fix #73 by @pietroppeter in #75
• Improve docs for section element (implicit path) and more info on srcDir -> homeDir logic by @pietroppeter in #72

Full Changelog: v0.3.0...v0.3.1