Update explicit tags for proper Apple/Google format#327

Merged

mattstratton merged 2 commits intomattstratton:masterfrom chrisreddington:itunes-explicit-fix

Dec 22, 2020

+6-6

Commits on Dec 13, 2020

Fixes #326 with no impact to current frontmatter docs
chrisreddington
committed

Commits on Dec 15, 2020

Adjustment to allow yes/no/true/false on explicit
chrisreddington
committed