To reserve space for the type traits sharing the same name as the ones
from standard library.

string_view_metadata was introduced to make compiled format relocatable.
However, format string compilation is an optimization and therefore
adding overhead and extra complexity for relocation is undesirable.
In most cases the string will be either static or outlive compilation
and formatting and if it doesn't, it's possible to make compiled
representation relocatale by other means.

using instead of typedef.

climits instead of limits.h

Added missing cast to size_t.

* Map not int enum to correct underlying_type

* Use non-zero constant in TestFixedEnum

test cuda: import fmt in CUDA source code

Current test is only for Windows(cl.exe).
Need to test more with the other host compilers...

* Activate the test when `find_package(CUDA)` worked
* The test runs with C++14

Detailed comments in 'test/cuda-test'

test cuda: add more comment / macro check

* checks both `__NVCC__` and `__CUDACC__`

More comments for CMake and CUDA source file.

test cuda: <fmt/core.h> checks NVCC and CUDA

The header file checks 2 things.

* __NVCC__: if the compiler is from NVIDIA
* __CUDACC__: if the source code is CUDA(.cu) file

Since we can't sure all users prefer latest, Version for
`find_pacakge(CUDA)` is downgraded to 9.0.
This is the minimum version for C++14 in CUDA

To avoid clang warning:

fmtlib/include/fmt/chrono.h:753:32: error: declaration shadows a field of 'formatter<duration<type-parameter-0-0, type-parameter-0-1>, type-parameter-0-2, void>' [-Werror,-Wshadow]