Radiation calculation from Particle Trajectories

[skuschel]

All routines should be placed in a new module postpic.radiation which is located at postpic/radiation.py. May require cython optimizations. There should be a general interface to be used even without postpic plus some convenience routines to be used with the particle history class. Algortithms and optimizations are the priority.

It also needs to be tests what performance these routines provide. If they are really computationally expensive, the underlying C-Code could make use of (thread) parallel version. A similar thing has been tested in the (outdated) cythonparallel branch. But this is a second step. Lets first see how far we can push performance on a single thread and if this becomes a bottleneck at all.

[skuschel]

needs proper example data: #45

[skuschel]

Current status in www.github.com/ra3dnr/postpic/tree/synthspec