hints: expose as C kr_rule_local_*()

hints: expose as C kr_rule_local_*()

At least the normal non-root hints.
We needed extended API for this functionality, and C API is simpler
for this, thanks to LuaJIT FFI.

However, this required moving code from the separate module.
The moved code is not changed in any way in this commit.
I considered it bad to keep such core code outside the main daemon+lib,
as it's not big.  Now LuaJIT FFI forced me to clean this up.