[docs] Added srt_getversion() API documentation

docs/API-functions.md

@@ -24,6 +24,7 @@ SRT API Functions
   * [srt_getsockname](#srt_getsockname)
   * [srt_getsockopt, srt_getsockflag](#srt_getsockopt-srt_getsockflag)
   * [srt_setsockopt, srt_setsockflag](#srt_setsockopt-srt_setsockflag)
+  * [srt_getversion](#srt_getversion)
 - [**Helper data types for transmission**](#Helper-data-types-for-transmission)
   * [SRT_MSGCTRL](#SRT_MSGCTRL)
 - [**Transmission**](#Transmission)
@@ -544,11 +545,29 @@ type with the option value to be set.
 
 -Errors:
 
-  * `SRT_EINVSOCK`: Socket `u` indicates no valid socket ID
+  * `MN_INVAL`: Socket `u` indicates no valid socket ID
   * `SRT_EINVOP`: Option `opt` indicates no valid option
   * Various other errors that may result from problems when setting a specific 
   option (see option description for details).
 
+### srt_getversion
+
+```
+int srt_getversion(void* val, int len);
+```
+
+Get SRT version value. The version format in hex is 0xXXYYZZ for x.y.z in human readable form, 
+where x = ("%d", (version>>16) & 0xff), etc.
+
+- Returns:
+
+  * `SRT_ERROR` (-1) in case of error, otherwise 0
+
+-Errors:
+
+  * `SRT_EINVPARAM` invalid parameters were passed to the function
+
+
 Helper data types for transmission
 ----------------------------------