Lattice construction and degenerate matrices

[ExpHP]

    // FIXME API in limbo, it should do one of the following:
    //  * have new() return Lattice, make `inverse` a lazy Option,
    //      make `inverse_matrix` and `inverted` return Results
    //  * have new() return Result, with `inverse` strictly computed as it is now
    /// Create a lattice from a matrix where the rows are lattice vectors.
    pub fn new(matrix: &[[f64; 3]; 3]) -> Self {
        ...
    }