Update AmebaPro2 Example Guide and API (Ameba-AIoT#27)

* Update Amebapro2 Example Guide and API

- Update Class VideoStreamOverlay
- Add RTSP Streaming with OSD Image Example Guide
- Add Object Detection results save on SD Card example guide

* Update DDR_used.rstt

Author: pammyleong

source/FAQ/DDR_used.rst

@@ -1,6 +1,6 @@
 .. tags:: DDR, AMB82-mini
 
-Which DDR is used by AME82-mini? DDR2 or DDR3?
+Which DDR is used by AMB82-mini? DDR2 or DDR3?
 ==============================================
 
 We set up the internal memory with DDR2 (1.8 V), but after checking the datasheet, we are unsure if this is the right configuration or the difference with the DDR3L (1.35 V).