Jira2markdown

- feat(text-effects): use `<u>` tag in markdown to convert underline token https://github.com/catcombo/jira2markdown/issues/14
- feat(links): add support for email tags

- add optional space indentation for the list items https://github.com/catcombo/jira2markdown/issues/9

- upgrade `pyparsing` to version 3
- update minimal Python version to 3.7
- horizontal rule loses trailing and leading spaces after conversion

- parse optional parameters for `code` and `noformat` tags
- improve language name parsing for `code` tag

- Massive improvements in parsing of all elements
- Add parser elements [customization](https://github.com/catcombo/jira2markdown#customization)

- Add new conversions for:
- `??citation??`
- `^superscript^`
- `~subscript~`
- `{panel}...{panel}`
- Add space before and after user mention (`username`) if it adjacent to a text
- Allow punctuation marks come after the user mention (`username`) without a space
- Add a line break before and after a table if only it adjacent to a text