prepare for ins preview in system file picker

papers/newIns.md

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+# possible new Furnace instrument format
+
+the main issue with Furnace instrument files is that they are too big, even if the instrument is nothing more than the FM setup...
+
+the aim of this new format is to greatly reduce the size of a resulting instrument.
+
+```
+size | description
+-----|------------------------------------
+  6  | "FURINS" format magic
+  2  | format version
+  1  | instrument type
+ ??? | feature bits
+  4  | instrument length (if wave/sample bits are on)
+```
+
+the "feature bits" field is a variable length bitfield. bit 7 in a byte indicates "read one more byte".
+
+the feature bits are:
+
+- 0: has wavetables
+- 1: has samples
+- 2: has name
+- 3: FM data
+- 4: FM data size (1: 2-op, 0: 4-op)
+- 5: FM data includes OPL/OPZ data
+  - if off, only read an op until ssgEnv.
+  - if on, read everything else.
+- 6: Game Boy data
+- 7: (continue in next byte)
+- 8: C64 data
+- 9: Amiga data
+- 10: standard data (macros)
+- 11: operator macros
+- 12: release points
+- 13: op release points
+- 14: extended op macros
+- 15: (continue in next byte)
+- 16: OPL drums mode data
+- 17: Amiga sample map data
+- 18: Namco 163 data
+- 19: extra macros
+- 20: FDS data
+- 21: OPZ data
+- 22: wavetable synth data
+- 23: (continue in next byte)
+- 24: additional macro modes
+- 25: extra C64 data
+- 26: MultiPCM data