time: Introduce "real" struct_time.

Implemented using namedtuple and lacks tm_zone, tm_gmtoff fields.

time/time.py

@@ -1,4 +1,5 @@
 from utime import *
+from ucollections import namedtuple
 import ustruct
 import uctypes
 import ffi
@@ -16,6 +17,8 @@ localtime_ = libc.func("P", "localtime", "P")
 strftime_ = libc.func("i", "strftime", "sisP")
 mktime_ = libc.func("i", "mktime", "P")
 
+_struct_time = namedtuple("struct_time",
+    ["tm_year", "tm_mon", "tm_mday", "tm_hour", "tm_min", "tm_sec", "tm_wday", "tm_yday", "tm_isdst"])
 
 def _tuple_to_c_tm(t):
     return ustruct.pack("@iiiiiiiii", t[5], t[4], t[3], t[2], t[1] - 1, t[0] - 1900, (t[6] + 1) % 7, t[7] - 1, t[8])
@@ -23,10 +26,10 @@ def _tuple_to_c_tm(t):
 
 def _c_tm_to_tuple(tm):
     t = ustruct.unpack("@iiiiiiiii", tm)
-    return tuple([t[5] + 1900, t[4] + 1, t[3], t[2], t[1], t[0], (t[6] - 1) % 7, t[7] + 1, t[8]])
+    return _struct_time(t[5] + 1900, t[4] + 1, t[3], t[2], t[1], t[0], (t[6] - 1) % 7, t[7] + 1, t[8])
 
 def struct_time(tm):
-    return tm
+    return _struct_time(*tm)
 
 
 def strftime(format, t=None):