Update to commonmark spec 0.29#156

Merged

robinst merged 22 commits intomasterfrom

issue-152-commonmark-0.29

Jul 12, 2019

Commits on Apr 12, 2019

Commits on Apr 15, 2019

Adapt link reference definition parsing to spec changes
robinst
committed

Commits on Jun 5, 2019

Extract link scanning logic and replace use of regexes
robinst
committed