Added mutability flag for by-element iterator
First use of immutable iterators
Used immutable by-element iterator for most operations
Added immutable transposed by-element iterator
Used immutable iterators in matrix multiplication
Merge branch 'const-iterators'
Added diagonalization of complex double hermitian (?) matrix
Tested diagonalization
Fixed matrix type check
Fixed checks for overloaded functions
Merge branch 'diagonalization'