Test Elements::NIST on travis
MO::Basis::LCAO#shells should return a collection of BasisSet::LCAO::Gaussian::Shells
Move to MO::Basis::LCAO::Gaussian
MO::Basis::LCAO::Gaussian#overlap should return a matrix
RuPHY::Math::Matrix#diagonal_elements
Define all_be_within matcher
Specs for MO::Basis::LCAO::Gaussian#overlap
Initialize shells
BasisSet::LCAO::Gaussian#shells
Spec for BasisSet::LCAO::Gaussian#shells
Downloaded STO-3G basisset from basisset exchange