devel/rubygem-gyoku: update to 1.4.0 and take maintainership

While here:
- Updated PORTVERSION to DISTVERSION
- Added rubygem-rexml, which prevents build failure
- Formatted the Makefile
- Added more description about the port

Changelog: https://github.com/savonrb/gyoku/blob/v1.4.0/CHANGELOG.md

PR:		288447
Reported by:	Atanu Biswas <atanubiswas484@gmail.com> (new maintainer)