cross sections on phase space points (#52)

With this PR, we adopt the phase space points from #51 for the
probability and cross section interface.

Further changes: we drop the support of different phase space
definitions for the in- and out-phase space.

⚠️ This is based on
https://github.com/AntonReinhard/QEDprocesses.jl/tree/phase_space_point
and should be rebased to `dev` and considered for merging *after* #51 is
merged.

---------

Co-authored-by: Anton Reinhard <[email protected]>
Co-authored-by: Uwe Hernandez Acosta <[email protected]>

Author: 3 people

src/QEDprocesses.jl

@@ -31,7 +31,7 @@ export AbstractCoordinateSystem, SphericalCoordinateSystem
 export AbstractFrameOfReference, CenterOfMomentumFrame, ElectronRestFrame
 export AbstractPhasespaceDefinition, PhasespaceDefinition
 export ParticleStateful, PhaseSpacePoint
-export spin, polarization, momentum, getindex
+export spin, polarization, particle_direction, particle_species, momentum, getindex
 export generate_phase_space
 
 using QEDbase
@@ -45,4 +45,5 @@ include("momentum_generation.jl")
 include("propagators.jl")
 include("probabilities.jl")
 include("cross_sections.jl")
+include("patch_QEDbase.jl")
 end