Fortran simple timer module

Changelog

Three timing methods are supported: CPU, clock, and date.

Among them, clock timing is only valid for a short period of time, overflow system_clock's count_max will start to have problems; date timing is based on data_and_time timing, which does not fully determine the leap year and actual month.
The date timing is based on data_and_time, which doesn't judge the leap year and the actual month, but uses 365.24 days as a year and 30.4375 days as a month, when timing in the same month, the program is accurate, and introduces a certain amount of error after more than one month.

The above program, in general scenarios, is considered sufficient.