Add only parse strikethrough double tilde option

Author: hanny-ph

Sources/Markdown/Parser/CommonMarkConverter.swift

@@ -620,6 +620,9 @@ struct MarkupParser {
         if !options.contains(.disableSourcePosOpts) {
             cmarkOptions |= CMARK_OPT_SOURCEPOS
         }
+        if options.contains(.onlyParseStrikethroughDoubleTilde) {
+            cmarkOptions |= CMARK_OPT_STRIKETHROUGH_DOUBLE_TILDE
+        }
 
         let parser = cmark_parser_new(cmarkOptions)
 

Sources/Markdown/Parser/ParseOptions.swift

@@ -30,5 +30,8 @@ public struct ParseOptions: OptionSet {
 
     /// Disable including a `data-sourcepos` attribute on all block elements during parsing.
     public static let disableSourcePosOpts = ParseOptions(rawValue: 1 << 4)
+
+    /// Only parse strikethroughs if surrounded by exactly 2 tildes.
+    public static let onlyParseStrikethroughDoubleTilde = ParseOptions(rawValue: 1 << 5)
 }