Add new time functions (PEP 564)

Author: sproshev

stdlib/3/time.pyi

@@ -92,3 +92,11 @@ if sys.version_info >= (3, 3):
         def clock_getres(clk_id: int) -> float: ...  # Unix only
         def clock_gettime(clk_id: int) -> float: ...  # Unix only
         def clock_settime(clk_id: int, time: float) -> None: ...  # Unix only
+
+if sys.version_info >= (3, 7):
+    def clock_gettime_ns(clock_id: int) -> int: ...
+    def clock_settime_ns(clock_id: int, time: int) -> int: ...
+    def monotonic_ns() -> int: ...
+    def perf_counter_ns() -> int: ...
+    def process_time_ns() -> int: ...
+    def time_ns() -> int: ...