CommonMark 0.17

Note: with this release, we have split off the reference implementations into separate repositories. The JavaScript implementation is in https://github.com/jgm/commonmark.js, and the C implementation is in https://github.com/jgm/cmark. This repository contains the spec and tools for formatting the spec and running tests against it.

Spec changes:

• Improved rule limiting intraword _ for emphasis and strong emphasis. To prevent intra-word emphasis, we used to check to see if the delimiter was followed/preceded by an ASCII alphanumeric. We now do something more elegant: whereas an opening * must be left-flanking, an opening _ must be left-flanking and not right-flanking. And so on for the other cases. All the original tests passed except some tests with Russian text with internal _, which formerly created emphasis but no longer do with the new rule. These tests have been adjusted. A few new test cases have been added to illustrate the rule.
• Added example with link break inside pointy braces (no link) (#295).
• Added spec example: loose list with blank line after fenced code (#285).