Add generic Cholesky decomposition and make Cholesky parametric on matrix type plus some fixes. Define tril! and triu! for AbstractMatrix and use elements instead of type to construct zeros. Also use elements for constructing zeros in getindex(Triangular).
Merge pull request #7236 from JuliaLang/anj/chol

Add generic Cholesky decomposition and make Cholesky parametric on matrix type