The header and routines defined there are also used in standalone_cpp
target built from cpp/main.cpp

```
(idp_2022) [08:27:56 ansatnuc04 onemkl_gemv]$ $(find . -name cmake-build)/standalone_cpp 1000 11
Solving 1000 by 1000 diagonal system with rank-11 perturbation.
Converged in : 11 , 11 , 11 , 11 , 11 , 11 ,
Wall-clock cg_solve execution times: 683.416 , 408.391 , 411.849 , 412.661 , 412.317 , 412.658 ,
Redisual norm squared: 9.15541e-25
(idp_2022) [08:28:20 ansatnuc04 onemkl_gemv]$ python sycl_timing_solver.py 1000 11
Solving 1000 by 1000 diagonal linear system with rank 11 perturbation.
    Name            Intel(R) UHD Graphics [0x9bca]
    Driver version  1.3.22992
    Vendor          Intel(R) Corporation
    Profile         FULL_PROFILE
    Filter string   level_zero:gpu:0

Using not in-order queue
0 (host_dt, device_dt)= (1156.8981241434813, 404.2941620000001)
1 (host_dt, device_dt)= (422.38221131265163, 404.5959500000001)
2 (host_dt, device_dt)= (423.1058154255152, 404.4037220000001)
3 (host_dt, device_dt)= (422.79740050435066, 403.78802800000005)
4 (host_dt, device_dt)= (424.4473725557327, 404.0881560000001)
5 (host_dt, device_dt)= (425.1241758465767, 404.55793600000004)
Converged in:  [11, 11, 11, 11, 11, 11]
Python solution residual norm squared: 3.5289368114384933e-25
```

README is also expanded.

Expose cpp_cg_solve used in standalone_cpp executable from Python.
Invoked that from Python script sycl_timing_solver.py

```bash
$ python sycl_timing_solver.py 1000 11
Solving 1000 by 1000 diagonal linear system with rank 11 perturbation.
    Name            Intel(R) UHD Graphics [0x9bca]
    Driver version  1.3.22992
    Vendor          Intel(R) Corporation
    Profile         FULL_PROFILE
    Filter string   level_zero:gpu:0

Using not in-order queue
0 (host_dt, device_dt)= (1157.4030127376318, 403.9605020000001)
1 (host_dt, device_dt)= (421.32044583559036, 403.45619400000004)
2 (host_dt, device_dt)= (420.66121101379395, 402.57058400000005)
3 (host_dt, device_dt)= (421.5433243662119, 402.9254920000001)
4 (host_dt, device_dt)= (421.9988752156496, 402.8818340000001)
5 (host_dt, device_dt)= (422.3589450120926, 402.63814600000006)
Converged in:  [11, 11, 11, 11, 11, 11]
Python solution residual norm squared: 3.2839902926527995e-25
0 (host_dt, device_dt)= (412.9443597048521, 403.6290000000001)
1 (host_dt, device_dt)= (413.7023724615574, 403.8434720000001)
2 (host_dt, device_dt)= (413.4188834577799, 403.1985620000001)
3 (host_dt, device_dt)= (413.85203413665295, 402.70404800000006)
4 (host_dt, device_dt)= (416.2806496024132, 404.0513040000001)
5 (host_dt, device_dt)= (417.43320040404797, 404.74999800000006)
Converged in:  [11, 11, 11, 11, 11, 11]
cpp_cg_solve solution residual norm squared: 3.218393087932091e-25
```