Beta-RC3 Release

This is the round up for the next pre-release of PIConGPU, **beta-rc3**.

Please refer to the [change log]() for the newest changes.

Releases highlights:
- parallel hdf5 output with libSplash 1.1
- ADIOS output support
- a good amount of bug fixes in both PIConGPU and libPMacc
- mapped memory support