Improve test coverage

[JordanCheney]

There are a number of functions that don’t have unit tests yet. 2 parts to this:

1. Add tests for core types that are missing them. In priority order that is Tensor, AlignedPtr, TensorView
2. Add code coverage metrics with gcov + coveralls

@kcheney1 this would be a good starting point for you! Take a look in include/tnt/core/impl/tensor_impl.hpp. Tests are inside of TEST_CASEs. Pick any function you like that doesn’t have a test after it. You can create a branch and make a pull request.

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