Update API comments, refine footprint of wasm loader (#256)

and fix issues of get native stack boundary

Author: wenyongh

core/iwasm/include/wasm_export.h

@@ -179,7 +179,9 @@ package_type_t
 get_package_type(const uint8_t *buf, uint32_t size);
 
 /**
- * Load a WASM module from a specified byte buffer.
+ * Load a WASM module from a specified byte buffer. The byte buffer can be
+ * WASM binary data when interpreter or JIT is enabled, or AOT binary data
+ * when AOT is enabled. If it is AOT binary data, it must be 4-byte aligned.
  *
  * @param buf the byte buffer which contains the WASM binary data
  * @param size the size of the buffer
@@ -225,11 +227,13 @@ wasm_runtime_set_wasi_args(wasm_module_t module,
  * Instantiate a WASM module.
  *
  * @param module the WASM module to instantiate
- * @param stack_size the default stack size of the module instance, a stack
- *        will be created when function wasm_runtime_call_wasm() is called
- *        to run WASM function and the exec_env argument passed to
- *        wasm_runtime_call_wasm() is NULL. That means this parameter is
- *        ignored if exec_env is not NULL.
+ * @param stack_size the default stack size of the module instance when the
+ *        exec env's operation stack isn't created by user, e.g. API
+ *        wasm_application_execute_main() and wasm_application_execute_func()
+ *        create the operation stack internally with the stack size specified
+ *        here. And API wasm_runtime_create_exec_env() creates the operation
+ *        stack with stack size specified by its parameter, the stack size
+ *        specified here is ignored.
  * @param heap_size the default heap size of the module instance, a heap will
  *        be created besides the app memory space. Both wasm app and native
  *        function can allocate memory from the heap. If heap_size is 0, the
@@ -286,7 +290,7 @@ wasm_runtime_create_exec_env(wasm_module_inst_t module_inst,
 /**
  * Destroy the execution environment.
  *
- * @param env the execution environment to destroy
+ * @param exec_env the execution environment to destroy
  */
 void
 wasm_runtime_destroy_exec_env(wasm_exec_env_t exec_env);
@@ -305,17 +309,18 @@ wasm_runtime_get_module_inst(wasm_exec_env_t exec_env);
  * Call the given WASM function of a WASM module instance with
  * arguments (bytecode and AoT).
  *
- * @param exec_env the execution environment to call the function
+ * @param exec_env the execution environment to call the function,
  *   which must be created from wasm_create_exec_env()
- * @param function the function to be called
+ * @param function the function to call
  * @param argc the number of arguments
- * @param argv the arguments.  If the function method has return value,
+ * @param argv the arguments. If the function has return value,
  *   the first (or first two in case 64-bit return value) element of
  *   argv stores the return value of the called WASM function after this
  *   function returns.
  *
  * @return true if success, false otherwise and exception will be thrown,
- *   the caller can call wasm_runtime_get_exception to get exception info.
+ *   the caller can call wasm_runtime_get_exception to get the exception
+ *   info.
  */
 bool
 wasm_runtime_call_wasm(wasm_exec_env_t exec_env,
@@ -330,8 +335,9 @@ wasm_runtime_call_wasm(wasm_exec_env_t exec_env,
  * @param argc the number of arguments
  * @param argv the arguments array
  *
- * @return true if the main function is called, false otherwise and exception will be thrown,
- *   the caller can call wasm_runtime_get_exception to get exception info.
+ * @return true if the main function is called, false otherwise and exception
+ *   will be thrown, the caller can call wasm_runtime_get_exception to get 
+ *   the exception info.
  */
 bool
 wasm_application_execute_main(wasm_module_inst_t module_inst,
@@ -346,8 +352,9 @@ wasm_application_execute_main(wasm_module_inst_t module_inst,
  * @param argc the number of arguments
  * @param argv the arguments array
  *
- * @return true if the specified function is called, false otherwise and exception will be thrown,
- *   the caller can call wasm_runtime_get_exception to get exception info.
+ * @return true if the specified function is called, false otherwise and
+ *   exception will be thrown, the caller can call wasm_runtime_get_exception
+ *   to get the exception info.
  */
 bool
 wasm_application_execute_func(wasm_module_inst_t module_inst,