PyHEADTAIL v1.7.0

• Particles: added z_beamframe attribute for space charge calculations.
• Particles: make z_beamframe settable
• Make _version.py git evaluation comply with PEP440.
• Using Makefile instead of unclear ./install script.
• Make generators and Particles conform with the Printing interface!
• Adding SilentPrinters to tests and making test_particles work …
• versioning: only amend 4th number if different from master version! …
• Introduced extract_slices method
• m_p has been eliminated
• Introduced machines.synchrotron...