Cuvec

- fix external allocation (https://github.com/python/cpython/pull/24283)

- catch exceptions
- update `__init__` keywords
- build updates
+ add `CUVEC_DEBUG` flag (default: `OFF`)
+ use CMake `add_compile_definitions`
- test updates
+ increase verbosity
- documentation updates
+ add contributing notes
* using editable install & `pytest`
- misc tidy
+ clean `asarray` implementation

- add `asarray` convenience for wrapping external libraries
- minor code tidy

- add external project usage documentation
- add more accurate build warning message

- add seamless `numpy`-like functionality
+ rename `cuvec.from_numpy()` => `cuvec.copy()`
+ make `cuvec.zeros()` and `cuvec.copy()` return `numpy.ndarray`-like objects
- fix potential installation errors
- add complete documentation
- add citation information

Unifying Python/C++/CUDA memory: Python buffered array <-> C++11 ``std::vector`` <-> CUDA managed memory.

- Provides creation functions
+ Python object
* `zeros`
* `from_numpy`
+ C++ vector
* `CuVec<T>` with identical interface as `std::vector<T>`
+ CPython API (castable to `PyObject *`)
* `PyCuVec<T> *PyCuVec_zeros(std::vector<Py_ssize_t> shape);`
* `PyCuVec<T> *PyCuVec_zeros_like(PyCuVec<T> *other);`
* `PyCuVec<T> *PyCuVec_deepcopy(PyCuVec<T> *other);`
- Quick start documentation
- 100% test coverage
- Allows CUDA-free installation for `sdist`

Requires a C++11 compiler, CUDA compiler, and an NVIDIA GPU with compute capability 3.5 or greater.
Python functionality requires Python 3.6 or greater.