* Added: `spdlog::get_level()` API function - like `logger::level()`, except for the name change
* Added: `spdlog::should_log()` API function - like `logger: should_log()`
The meaning of using quotes to #include is implementation defined, so it
may or not may be what we want. At least POSIX
(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html)
says: "headers whose names are enclosed in double-quotes ( "" ) shall be
searched for first in the directory of the file with the #include line",
so not what we want since "spdlog" ends up twice in the path.