[cmp] add ztsd image compression support

* Based on the latest Bled, which adds ztsd compression support.
* Note that initial extraction of the 512 bytes MBR is very slow, because is seems
  clear that ZSTD was never designed for fast init or processing small elements of
  data, but instead for post init large volume streaming.
* Also note that this code adds 400 KB to the Rufus executable *AFTER UPX COMPRESSION*!
  Hopefully, the BusyBox folks can come up with a better and smaller way to add zstd
  support, because it's clear that the method used by the current BusyBox proposal,
  which is to leave as much of the original code untouched, isn't for the best...
* Closes #2590.
* Closes #2620.
* Closes #2621.

src/vhd.c

@@ -104,6 +104,7 @@ static comp_assoc file_assoc[] = {
 	{ ".bz2", BLED_COMPRESSION_BZIP2 },
 	{ ".xz", BLED_COMPRESSION_XZ },
 	{ ".vtsi", BLED_COMPRESSION_VTSI },
+	{ ".zst", BLED_COMPRESSION_ZSTD },
 	{ ".ffu", BLED_COMPRESSION_MAX },
 	{ ".vhd", BLED_COMPRESSION_MAX + 1 },
 	{ ".vhdx", BLED_COMPRESSION_MAX + 2 },