Add functionality to Procar class (VASP output) because xml file is hard to read if it is too large.
Merge branch 'master' of https://github.com/materialsproject/pymatgen
Merge branch 'master' of https://github.com/materialsproject/pymatgen
Merge branch 'master' of https://github.com/materialsproject/pymatgen
Add tests for new methods in Procar class