solver-basic: fix a 32 bits print format of size_t

We convert the std::size_t into the std::uintmax_t before use the
printf for PRIuMAX.
hash: speedup x3 to build key

We use '0' + [0-9] instead of std::to_string to improve solve time.
efyj: improve portability for Win32 system

efyj project:

- static libefyj library with only public symbol.
- shared libefyj library with only public symbol.
- efyj program uses shared library for *n*x and static library for Win32
  system.
- Add a pkg-config efyj-x.y.pc file;