v0.3.0.rc1

Full Changelog

Closed issues:

• The 'use' element outputs 'xlink-href='，shoud it be xlink:href=? #45

Merged pull requests:

• Allow setting attributues after initialization #48 (DannyBen)
• Test with GitHub Actions #44 (DannyBen)
• Configure better code hub #43 (DannyBen)
• Test with Ruby 2.7 #42 (DannyBen)
• Add support and contribution info #41 (DannyBen)
• Add link to "victor-opal" on README #40 (kuboon)