Implement common external function handlers in jerry-ext (#1787)

Added `handler` module to `jerry-ext` to contain implementation of
commonly used external function handlers: `assert`, `gc`, and
`print`.

Also adapted jerry-main to use jerry-ext/handler

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

jerry-ext/CMakeLists.txt

@@ -20,7 +20,12 @@ project (${JERRY_EXT_NAME} C)
 set(INCLUDE_EXT "${CMAKE_CURRENT_SOURCE_DIR}/include")
 
 # Source directories
-file(GLOB SOURCE_EXT arg/*.c)
+file(GLOB SOURCE_EXT_ARG      arg/*.c)
+file(GLOB SOURCE_EXT_HANDLER  handler/*.c)
+
+set(SOURCE_EXT
+    ${SOURCE_EXT_ARG}
+    ${SOURCE_EXT_HANDLER})
 
 add_library(${JERRY_EXT_NAME} STATIC ${SOURCE_EXT})