Most relevant commits:
- compiler/ast: document that URL node also represents an URL in Markdown
- compiler/ast: rename Extends.Context field to Format with Format type
- compiler/ast: remove 'URL.Context' field
- templates/builtin: panic parsing invalid regexp instead of fatal
- templates/builtin: add unmarshalJSON builtin function
- templates/builtin: prefix errors with builtin name
- templates/builtin: panic string instead of error in regexp builtin
- templates/builtin: add 'form' builtin variable