Update document and fix wasm_runtime_call_wasm_a issue (#1005)

Update document memory_tune.md: fix embed wamr link error,
fix description error of wasm operand stack size, update picture.

Fix wasm_runtime_call_wasm_a issue reported by #1003 and update
sample basic to call this API.

samples/basic/build.sh

@@ -22,7 +22,7 @@ cd ${CURR_DIR}
 mkdir -p cmake_build
 cd cmake_build
 cmake ..
-make
+make -j ${nproc}
 if [ $? != 0 ];then
     echo "BUILD_FAIL basic exit as $?\n"
     exit 2