v0.10.0 Enumerated Elements

• Moved from string based elements to enums see Element, this means that the Atom::set_element, Atom::element, and Term::element have changed
• Deprecated the following functions Atom::atom_number, Atom::atomic_radius, Atom::covalent_bond_radii,
  and Atom::vanderwaals_radius the radius functions are replaced with Element::atomic_radius which contains
  all these measures in the struct AtomicRadius
• Added Element::weight and Element::electro_negativity data
• Implemented Extend for all levels in the PDB hierarchy
• Implemented FromIterator for the PDB struct
• Removed requirement for atom_site.pdbx_formal_charge, atom_site.group_PDB, atom_site.occupancy, and atom_site.B_iso_or_equiv for mmCIF files (thanks to #93)
• Added support for SCALE, ORIGX, and MTRIX in mmCIF files (open and save)
• Fixed ignoring some of the auth_* series of mmCIF columns, by giving them precedence over the label_* columns in seq_id and asym_id (thanks to #95)
• Fixed remark-type-number 400 missing from the valid number list (thanks to #96)
• Fixed a small bug in saving MtriX records (thanks to #96)