v0.3.0

Fixes and improvements:

• 🚀 properly using multiple sub-interpreters simultaneously
• 🧓 added legacy_mode config knob to allow toggling to a mode that should support NumPy

Still todo:

• wire in a message batch mode to reduce overhead
• push more interpreter state handling into the runtime and maybe back up into https://github.com/voutilad/gogopython