v1.2.0

Bugfixes, documentation and new features, including:

• Improved boundary conditions, including scale-length extrapolation, wall recycling, neutral fast and thermal reflection. @mikekryjak
• New Ar, Ne, N, C cooling curves for fixed fraction simulations @mikekryjak
• Time-dependent density and power sources @mikekryjak
• classical_diffusion component @bendudson
• Stellarator 2-point model @bshanahan
• Flow, collision and reaction diagnostic outputs @mikekryjak
• Reaction multipliers to scale up/down specific reactions @mikekryjak
• Fixed calculation of polarization and diamagnetic drift ion energy exchange @bendudson
• TCV-X21 turbulence case inputs and analysis scripts @bendudson
• New tests, including electron drift-wave @bendudson
• CMake install now installs the hermes-3 executable