Fork 自IterativeSolvers.jl。存在以下改动：
- Verbose 动态输出增加相对残差列，使收敛速度更直观；
- gmres 求解器的基向量空间允许 AbstractArray 以方便移植。
IterativeSolvers is a Julia package that provides iterative algorithms for solving linear systems, eigensystems, and singular value problems.
To install the package, open the package manager in the REPL via ] and run
pkg> add IterativeSolvers