Refactor errors in tor-netdoc
This branch removes some unused error types, splits out parsing errors from building errors, and (most significantly) revises the tor-netdoc parsing Error type to be a struct that contains a new ParseErrorKind type.
This branch removes some unused error types, splits out parsing errors from building errors, and (most significantly) revises the tor-netdoc parsing Error type to be a struct that contains a new ParseErrorKind type.