Allow more sound effects and instruments

[pinobatch]

There's a request from darkhog to expand the sound effects table beyond 64 entries. I've seen analogous requests elsewhere to expand instruments beyond 51 entries. Doing this efficiently (that is, without 16-bit math every frame) might involve transposing pently_sfx_table and pently_instruments from their present array-of-structures layout to a structure-of-arrays. I want to do it, but I'll hold it for Pently 6 when I can do more breaking changes to data formats.