Another WHDLoad.hdf update

Created by: sonninnos

WHDLoad:

• Changed WHDLoad.hdf filesystem from OFS to FFS Closes #204 (closed)
• Slave ReadMe will be opened with MuchMore before running MkCustom

Other:

• Savestate tunings
  • Hopefully fixes crash on macos
  • Apparently fixed a long running problem with random savestate corruption
  • Silenced some logging verbosity

The savestate problem:

1. retro_serialize used size (based on what retro_serialize_size returns) to fread the temporary savefile
2. Actual savestate size may not be the same later on => Some parts are not read or vice versa

Size for fread is now taken directly from the just created temp file. No problems found yet.