SeetaResearch / Dragon

Summary:
This commit adds the ``memory_allocated`` API for ``dragon.Workspace``
to query the size of allocated memory (and optionally on a specified device).

Summary:
This commit enforces the algorithm finding even if the backward of filter or data
will not be executed. Otherwise, the empty algorithm will be encountered between
two cached operation with the same arguments and input shape.

Summary:
This commit removes the deprecated API for DALI 0.24.
Besides, variable length keyword arguments are added for forward compatibility.

Summary:
This commit fixes the issue on building with CUDA11 and CUDNN8.
Besides, C++14 is enabled by default instead of C++11 to support CUB 1.9+,
and for this reason, the compiler is required to be gcc5/clang6/msvc141 or higher.

Summary:
This commit uses sphinx to generate C++ API documentation
whose style and theme are consistent with the Python API.

Summary:
This commit computes the correct device for an existing output tensor.

Summary:
This commit enforces all the vm packages to take api/core structure
to adapt to the more complex future developments.

Summary:
This commit correctly passes the extra arguments
when executing a compiled graph function.

Summary:
This commit enforces the shape and data type inherited from the same metaclass,
which ensures the consistency between different styles.

Summary:
This commit normalizes the inconsistent math notations in docstring.

Summary:
This commit aligns the properties and methods of tensor class.

Summary:
This commit adds the clear method to free resources manually
if the workspace instance is referenced circularly.

Summary:
This commit moves the workspace api into the current workspace instance.
For this reason, the namespace ``dragon.workspace`` is removed for simplicity.

Summary:
This commit tests the executing of native ops and verifies the results.
Several bugs are found and fixed according to these tests.

Summary:
This commit removes the redundant workspace reference
when executing a tensor operation.

Summary:
We forgot to handle the inplace case that generated
the random elements on the output(i.e. the input).

Besides, this commit also fixes the omitted `RunOnDevice` for cudnn activations,
which will rightly dispatches the implementation.