Equation system

The layout of the unknowns, the equation terms, the equations and the system M du/dt = rhs(u, t) with its Jacobians.

Unknown layout: src/system/layout.jl
Equation terms: src/system/terms.jl, src/system/algebraic_terms.jl, src/system/moment_terms.jl, src/system/fokker_planck_terms.jl, src/system/knockon_terms.jl, src/system/interface_term.jl, src/system/transport_terms.jl, src/system/population_terms.jl, src/system/avalanche_terms.jl, src/system/energy_terms.jl, src/system/radiation_terms.jl, src/system/heat_transport_terms.jl, src/system/ion_energy_terms.jl, src/system/ion_terms.jl, src/system/kinetic_ionization.jl
Conductivity and induction: src/system/conductivity_terms.jl, src/system/induction_terms.jl
Energy transfer between the distributions: src/system/energy_transfer_terms.jl
Equations and the system: src/system/equations.jl, src/system/equation_system.jl
Jacobians: src/system/jacobian.jl