Preload data folder to RAM

[DCxDemo]

In case PKR file is dummied out, as an alternative to #35, should also be able to preload all files from data folder to RAM.
Kinda like DuckStation does with ROMs, a longer initial loading trade off for faster level/skater swaps. should be kinda instant in fact.

guess should use a hash table of { filenameHash, ptrFile }. can use original WAD checksum for that.