eml_parser: Recursion DoS via nested message/rfc822 attachments

eml_parser serves as a python module for parsing eml files and returning various information found in the e-mail as well as computed information. Prior to 3.0.1, EmlParser.get_raw_body_text() recurses unconditionally for every nested message/rfc822 attachment without any depth limit. An attacker who can supply a badly crafted EML file with approximately 120 nested message/rfc822 parts triggers an unhandled RecursionError and aborts parsing of the message. A 12 KB EML file is enough to crash a worker. Though this causes the parser to crash, it is an unlikely scenario as the suggested EML that crashes the parser would not pass basic RFC compliance tests. This vulnerability is fixed in 3.0.1.