Added support for multi-target assign, `break` and `continue` statements

What's Changed

• Cleaned up graph code by @WorldofKerry in #161
• Added support for multi-target assign by @WorldofKerry in #162
• Replaced frontend generator parser with improved version that has more semantics by @WorldofKerry in #163
• Experimenting with parsing from text, incremented version number by @WorldofKerry in #164

Full Changelog: v0.2.6...v0.2.8