Change name to to findFrameCompressedSize and add skippable support

lib/legacy/zstd_v01.h

@@ -40,7 +40,7 @@ ZSTDv01_getFrameSrcSize() : get the source length of a ZSTD frame compliant with
     return : the number of bytes that would be read to decompress this frame
              or an errorCode if it fails (which can be tested using ZSTDv01_isError())
 */
-size_t ZSTDv01_getFrameCompressedSize(const void* src, size_t compressedSize);
+size_t ZSTDv01_findFrameCompressedSize(const void* src, size_t compressedSize);
 
 /**
 ZSTDv01_isError() : tells if the result of ZSTDv01_decompress() is an error