created zstd_decompress_block module

isolate all logic associated with block decompression
into its own module.

zstd_decompress is still in charge
of context creation/destruction,
frames, headers, streaming, special blocks, etc.

Compressed blocks themselves are now handled within zstd_decompress_block .

build/VS2008/fuzzer/fuzzer.vcproj

@@ -412,6 +412,10 @@
 				RelativePath="..\..\..\lib\decompress\zstd_decompress.c"
 				>
 			</File>
+			<File
+				RelativePath="..\..\..\lib\decompress\zstd_decompress_block.c"
+				>
+			</File>
 			<File
 				RelativePath="..\..\..\lib\decompress\zstd_ddict.c"
 				>