flexmark-java extension for definition list processing

Converts definition syntax of Php Markdown Extra Definition List into `<dl></dl>` html

Definition items can be preceded by `:` or `~`

Definition list is one or more definition terms with one or more definitions.

    Definition Term
    : Definition of above term
    : Another definition of above term

Definitions terms can have no definitions if they are not the last term before a definition:

    Definition Term without definition
    Definition Term
    : Definition of above term
    : Another definition of above term