Decompressed size functions now handle multiframes and distinguish cases

- Add ZSTD_findDecompressedSize
    - Traverses multiple frames to find total output size
- Add ZSTD_getFrameContentSize
    - Gets the decompressed size of a single frame by reading header
- Deprecate ZSTD_getDecompressedSize

examples/simple_decompression.c

@@ -63,7 +63,7 @@ static void decompress(const char* fname)
 {
     size_t cSize;
     void* const cBuff = loadFile_X(fname, &cSize);
-    unsigned long long const rSize = ZSTD_getDecompressedSize(cBuff, cSize);
+    unsigned long long const rSize = ZSTD_findDecompressedSize(cBuff, cSize);
     if (rSize==0) {
         printf("%s : original size unknown. Use streaming decompression instead. \n", fname);
         exit(5);