v0.9.0

What's Changed

• Add a Weight object that encapsules a scalar by @florianwechsung in #230
• Improvements to RegularGridInterpolant3D and C++ documentation #103 by @florianwechsung in #227
• Setup numpy dependency in the recommended way by @mbkumar in #234
• Update branch by @rogeriojorge in #236
• Save and load coils by @landreman in #235
• Principal curvatures by @ejpaul in #232
• Expanded coil documentation by @rogeriojorge in #237
• JSON serialization by @mbkumar in #231

Full Changelog: v0.8.0...v0.9.0