climlab/climlab: Version 0.8.1

A major refactor of the internals: all the Fortran code has been moved into external companion packages climlab-rrtmg, climlab-cam3-radiation, and climlab-emanuel-convection. Climlab is now (once again!) a pure Python package. Builds of these helper packages are available through conda-forge and will be automatically installed as dependencies by conda / mamba.

The climlab source repo also moved to https://github.com/climlab/climlab

There should be no breaking changes to the user-facing API.

The major motivation for this change was to (vastly) simplify the development and testing of new-and-improved climlab internals (coming soon).