GitLab

Removes numpy dependency from test_gpu.py test and re-enables Python tests for Python 3.6.

The inaccuracy was caused by ONNX round requires nearest integer rounding for halway (0.5) cases.
std::round rounds away from zero, thus giving wrong results with halfway cases.
Replaced std::round with std::nearbyint which uses the correct rounding by default.

Fixes an issue that comes up for variable input slice with steps set manually in ONNX to default 1's.

Simplifies dimensions_of instructions to a literal when possible.
Intended to be used after the split_single_dyn_dim pass.