Add soft assert handler to jerry-ext (#2516)

Allow developers to choose whether they want a hard or a soft
implementation behind `assert`, i.e., whether they want to kill
the whole engine in case of an assertion failure in the executed
script or just throw a JS error.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

docs/10.EXT-REFERENCE-HANDLER.md

@@ -1,17 +1,17 @@
 #  Common external function handlers
 
-## jerryx_handler_assert
+## jerryx_handler_assert_fatal
 
 **Summary**
 
-Assert for scripts. The routine calls `jerry_port_fatal` on assertion failure.
+Hard assert for scripts. The routine calls `jerry_port_fatal` on assertion failure.
 
 **Prototype**
 
 ```c
 jerry_value_t
-jerryx_handler_assert (const jerry_value_t func_obj_val, const jerry_value_t this_p,
-                       const jerry_value_t args_p[], const jerry_length_t args_cnt);
+jerryx_handler_assert_fatal (const jerry_value_t func_obj_val, const jerry_value_t this_p,
+                             const jerry_value_t args_p[], const jerry_length_t args_cnt);
 ```
 
 - `func_obj_val` - the function object that was called (unused).
@@ -27,6 +27,43 @@ jerryx_handler_assert (const jerry_value_t func_obj_val, const jerry_value_t thi
 - [jerryx_handler_register_global](#jerryx_handler_register_global)
 
 
+## jerryx_handler_assert_throw
+
+**Summary**
+
+Soft assert for scripts. The routine throws an error on assertion failure.
+
+**Prototype**
+
+```c
+jerry_value_t
+jerryx_handler_assert_throw (const jerry_value_t func_obj_val, const jerry_value_t this_p,
+                             const jerry_value_t args_p[], const jerry_length_t args_cnt);
+```
+
+- `func_obj_val` - the function object that was called (unused).
+- `this_p` - the `this` value of the call (unused).
+- `args_p` - the array of function arguments.
+- `args_cnt` - the number of function arguments.
+- return value - `jerry_value_t` representing boolean true, if only one argument
+  was passed and that argument was a boolean true, an error otherwise.
+
+**See also**
+
+- [jerryx_handler_register_global](#jerryx_handler_register_global)
+
+
+## jerryx_handler_assert_fatal
+
+**Summary**
+
+An alias to `jerryx_handler_assert_fatal`.
+
+**See also**
+
+- [jerryx_handler_assert_fatal](#jerryx_handler_assert_fatal)
+
+
 ## jerryx_handler_gc
 
 **Summary**