Add ZSTD_CCtx_resetParameters() function

* Fix docs for `ZSTD_CCtx_reset()`.
* Add `ZSTD_CCtx_resetParameters()`.

Fixes #1094.

lib/compress/zstd_compress.c

@@ -72,9 +72,11 @@ ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem)
     {   ZSTD_CCtx* const cctx = (ZSTD_CCtx*)ZSTD_calloc(sizeof(ZSTD_CCtx), customMem);
         if (!cctx) return NULL;
         cctx->customMem = customMem;
-        cctx->requestedParams.compressionLevel = ZSTD_CLEVEL_DEFAULT;
-        cctx->requestedParams.fParams.contentSizeFlag = 1;
         cctx->bmi2 = ZSTD_cpuid_bmi2(ZSTD_cpuid());
+        {   size_t const err = ZSTD_CCtx_resetParameters(cctx);
+            assert(!ZSTD_isError(err));
+            (void)err;
+        }
         return cctx;
     }
 }
@@ -671,6 +673,12 @@ void ZSTD_CCtx_reset(ZSTD_CCtx* cctx)
     cctx->cdict = NULL;
 }
 
+size_t ZSTD_CCtx_resetParameters(ZSTD_CCtx* cctx)
+{
+    if (cctx->streamStage != zcss_init) return ERROR(stage_wrong);
+    return ZSTD_CCtxParams_reset(&cctx->requestedParams);
+}
+
 /** ZSTD_checkCParams() :
     control CParam values remain within authorized range.
     @return : 0, or an error code if one value is beyond authorized range */