VerthashMiner v0.7.1

- Changed "difficulty to target" formula to a more reliable one.
- Miner will no longer load NVML and ADL libraries when they are not needed.
- OpenCL back-end will now report error codes along with messages.
- Fixed NVIDIA OpenCL devices restrictions when compiled with CUDA 10 or lower.
- Added GPU memory errors tracker. Invalid shares will be discarded.
- Lowered ADL library version requirements.
- Lowered CMake version requirements.