add documentation and comments

Documentation/pycardium/utime.rst

@@ -28,6 +28,11 @@ alarm.
    Return the current timestamp in seconds since 2000-01-01 00:00 in
    the local timezone.
 
+.. py:function:: time_ms()
+
+   Return the current timestamp in milliseconds since 2000-01-01 00:00 in
+   the local timezone.
+
 .. py:function:: set_time(secs)
 
    Sets the time to ``secs`` seconds since 2000-01-01 00:00 in the local

epicardium/epicardium.h

@@ -1567,7 +1567,7 @@ API(API_FILE_MKDIR, int epic_file_mkdir(const char *dirname));
 API(API_RTC_GET_SECONDS, uint32_t epic_rtc_get_seconds(void));
 
 /**
- * Read the current RTC value.
+ * Read the current RTC value in ms.
  *
  * :return: Unix time in milliseconds
  */