Use INT*_C and UINT*_C macros for special integer constants.

SSIA.
following points are worth to consider, IMHO.
* unify Knuth's multiplicative hash.
* define markers which are commonly used in `src/tree.c` and `src/type.c`.
* clean up some integer usage like `unsigned` and `int`.  
  replace `size_t` and `ssize_t` looks better in some cases, but this change will affect function decls/calls.