Libc/os/run/rand/io reorganization. Close #1373. Close #1638.
- Move io, run and rand to core.
- Remove incorrect ctypes module (use libc).
- Remove os-specific modules for os and fs.
- Split fs between core::path and core::os.
Merge all 3 log syntaxes, tidy up residual misuses.
Copy first batch of material from libstd to libcore.