* Allow disabling floating point support
Add FMT_USE_FLOAT, FMT_USE_DOUBLE and FMT_USE_LONG_DOUBLE to allow a
user of the library to configure the float types they want to allow.
This is specially useful in embedded environements where code size is
important.
* Avoid conditional macros to disable float support
* Add is_supported_floating_point constexpr function
* Fix empty-body warning