v2019.5.28

• New VASP Input Set "from previous" interface (@utf)
• ELFCAR support (@mkhorton)
• Improvements to plotting of band structures and densities of states (@ShuaishuaiYuan)
• Convenience functions added to Composition including chemical system convention (@mkhorton)
• Various bug fixes (@mkhorton, @utf)
• Improvements to MEGNET API (@shyuep)
• Improvements to Structure interpolation (@mturiansky)