Merge pull request #108 from atusy/release-v0.6.4

release v0.6.4

chore(release): submit v0.6.3 to CRAN

Merge pull request #98 from atusy/horizontal-rule

fix(ast): avoid error on HorizontalRule with a fallback and a warning

release: v0.6.1

chore: release 0.6.0

release 0.5.0

release 0.4.0

release 0.3.0 on CRAN

release 0.2.0 on CRAN

release 0.1.1