v0.12.0 Matrices and CI hooks

Large update with rewriting amplitude computation with matrix operations, and a great cleaning up the code by hooks.

What's Changed

• Minor-methods: y2σs and lims by @mmikhasenko in #37
• Mandelstam typo and CI hooks by @mmikhasenko in #38
• Full amplitude as matrix by @mmikhasenko in #36

Full Changelog: v0.11.3...v0.12.0