add BROTLI_DEC_API to methods (#572)

diff --git a/c/include/brotli/decode.h b/c/include/brotli/decode.h
index b18e9e4..356edd1 100755
--- a/c/include/brotli/decode.h
+++ b/c/include/brotli/decode.h
@@ -327,7 +327,7 @@
  *          the input and produced all of the output
  * @returns ::BROTLI_FALSE otherwise
  */
-BROTLI_BOOL BrotliDecoderIsFinished(const BrotliDecoderState* state);
+BROTLI_DEC_API BROTLI_BOOL BrotliDecoderIsFinished(const BrotliDecoderState* state);
 
 /**
  * Acquires a detailed error code.
@@ -340,7 +340,7 @@
  * @param state decoder instance
  * @returns last saved error code
  */
-BrotliDecoderErrorCode BrotliDecoderGetErrorCode(
+BROTLI_DEC_API BrotliDecoderErrorCode BrotliDecoderGetErrorCode(
     const BrotliDecoderState* state);
 
 /**