Improve the jerry port api documents. (#4977)

Notable changes:
  - Remove the comments in port impl, that's easily getting to in-consistence
  - Sync the jerryscript-port.h and 05.PORT-API.md
  - Fixes the invalid comment in port codes

JerryScript-DCO-1.0-Signed-off-by: Yonggang Luo luoyonggang@gmail.com

targets/os/mbedos/jerry-port.cpp

@@ -20,20 +20,14 @@
 
 #include "mbed.h"
 
-/**
- * Aborts the program.
- */
 void
 jerry_port_fatal (jerry_fatal_code_t code)
 {
   exit ((int) code);
 } /* jerry_port_fatal */
 
-/**
- * Provide log message implementation for the engine.
- */
 void
-jerry_port_log (const char *message_p) /**< message */
+jerry_port_log (const char *message_p)
 {
   while (*message_p != '\0')
   {
@@ -47,11 +41,6 @@ jerry_port_log (const char *message_p) /**< message */
   }
 } /* jerry_port_log */
 
-/**
- * Dummy function to get the time zone adjustment.
- *
- * @return 0
- */
 int32_t
 jerry_port_local_tza (double unix_ms)
 {
@@ -60,11 +49,6 @@ jerry_port_local_tza (double unix_ms)
   return 0;
 } /* jerry_port_local_tza */
 
-/**
- * Implementation of jerry_port_current_time.
- *
- * @return current timer's counter value in milliseconds
- */
 double
 jerry_port_current_time (void)
 {