Emittance calculation

Hello, There are a few changes that need to be verified. I've changed the way emittance is computed. For nonzero dispersion, it gives the correct results. When dispersion is included, I think the difference is minimal for realistic values. But I am not sure.

• Calculation of emittances and CS invariants for nonzero dispersion (based on PyHEADTAIL "cobra" functions)
• Different ion species data in impedance.ions

docs/source/conf.py

@@ -12,6 +12,7 @@
 #
 import os
 import sys
+
 sys.path.insert(0, os.path.abspath('.'))
 sys.path.insert(0, os.path.abspath("../"))
 sys.path.insert(0, os.path.abspath("../../"))