Switched to 'time' from 'datetime' library for time utility functions

based on the advices of @jeremydouglass and @gvrancken. I have switched from 'datetime' to 'time' to improve performance.

Related to #129

p5/pmath/time.py

@@ -16,24 +16,24 @@
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 #
 
-import datetime
+import time
 import builtins
 
+
+def millis():
+	return int((time.perf_counter() - builtins.start_time)*1000)
+
 def day():
-	return datetime.datetime.now().day
+	return int(time.strftime("%d"))
 
 def hour():
-	return datetime.datetime.now().hour
-
-def millis():
-	return (datetime.datetime.now() - builtins.start_time).total_seconds()*1000
+	return int(time.strftime("%H"))
 
 def minute():
-	return datetime.datetime.now().minute
+	return int(time.strftime("%M"))
 
 def second():
-	return datetime.datetime.now().second
+	return int(time.strftime("%S"))
 
 def year():
-	return datetime.datetime.now().year
-
+	return int(time.strftime("%Y"))

p5/sketch/userspace.py

@@ -22,7 +22,7 @@
 import math
 import numpy as np
 import builtins
-import datetime
+import time
 from functools import wraps
 
 from vispy import app
@@ -154,7 +154,7 @@ def run(sketch_setup=None, sketch_draw=None, frame_rate=60, mode="P2D"):
 
     builtins.pixel_x_density = physical_width // width
     builtins.pixel_y_density = physical_height // height
-    builtins.start_time = datetime.datetime.now()
+    builtins.start_time = time.perf_counter()
 
     p5.sketch.timer.start()